CINXE.COM

<!DOCTYPE html> <html class='v2' dir='ltr' xmlns='http://www.w3.org/1999/xhtml' xmlns:b='http://www.google.com/2005/gml/b' xmlns:data='http://www.google.com/2005/gml/data' xmlns:expr='http://www.google.com/2005/gml/expr'> <head> <link href='https://www.blogger.com/static/v1/widgets/3566091532-css_bundle_v2.css' rel='stylesheet' type='text/css'/> <meta content='width=1100' name='viewport'/> <meta content='text/html; charset=UTF-8' http-equiv='Content-Type'/> <meta content='blogger' name='generator'/> <link href='http://www.righto.com/favicon.ico' rel='icon' type='image/x-icon'/> <link href='http://www.righto.com/2022/01/' rel='canonical'/> <link rel="alternate" type="application/atom+xml" title="Ken Shirriff's blog - Atom" href="http://www.righto.com/feeds/posts/default" /> <link rel="alternate" type="application/rss+xml" title="Ken Shirriff's blog - RSS" href="http://www.righto.com/feeds/posts/default?alt=rss" /> <link rel="service.post" type="application/atom+xml" title="Ken Shirriff's blog - Atom" href="https://www.blogger.com/feeds/6264947694886887540/posts/default" />  <meta content='http://www.righto.com/2022/01/' property='og:url'/> <meta content='Ken Shirriff's blog' property='og:title'/> <meta content='Computer history, restoring vintage computers, IC reverse engineering, and whatever' property='og:description'/> <title>Ken Shirriff's blog: January 2022</title> <style type='text/css'>@font-face{font-family:'Play';font-style:normal;font-weight:400;font-display:swap;src:url(//fonts.gstatic.com/s/play/v19/6aez4K2oVqwIvtg2H68T.woff2)format('woff2');unicode-range:U+0460-052F,U+1C80-1C8A,U+20B4,U+2DE0-2DFF,U+A640-A69F,U+FE2E-FE2F;}@font-face{font-family:'Play';font-style:normal;font-weight:400;font-display:swap;src:url(//fonts.gstatic.com/s/play/v19/6aez4K2oVqwIvtE2H68T.woff2)format('woff2');unicode-range:U+0301,U+0400-045F,U+0490-0491,U+04B0-04B1,U+2116;}@font-face{font-family:'Play';font-style:normal;font-weight:400;font-display:swap;src:url(//fonts.gstatic.com/s/play/v19/6aez4K2oVqwIvtY2H68T.woff2)format('woff2');unicode-range:U+0370-0377,U+037A-037F,U+0384-038A,U+038C,U+038E-03A1,U+03A3-03FF;}@font-face{font-family:'Play';font-style:normal;font-weight:400;font-display:swap;src:url(//fonts.gstatic.com/s/play/v19/6aez4K2oVqwIvto2H68T.woff2)format('woff2');unicode-range:U+0102-0103,U+0110-0111,U+0128-0129,U+0168-0169,U+01A0-01A1,U+01AF-01B0,U+0300-0301,U+0303-0304,U+0308-0309,U+0323,U+0329,U+1EA0-1EF9,U+20AB;}@font-face{font-family:'Play';font-style:normal;font-weight:400;font-display:swap;src:url(//fonts.gstatic.com/s/play/v19/6aez4K2oVqwIvts2H68T.woff2)format('woff2');unicode-range:U+0100-02BA,U+02BD-02C5,U+02C7-02CC,U+02CE-02D7,U+02DD-02FF,U+0304,U+0308,U+0329,U+1D00-1DBF,U+1E00-1E9F,U+1EF2-1EFF,U+2020,U+20A0-20AB,U+20AD-20C0,U+2113,U+2C60-2C7F,U+A720-A7FF;}@font-face{font-family:'Play';font-style:normal;font-weight:400;font-display:swap;src:url(//fonts.gstatic.com/s/play/v19/6aez4K2oVqwIvtU2Hw.woff2)format('woff2');unicode-range:U+0000-00FF,U+0131,U+0152-0153,U+02BB-02BC,U+02C6,U+02DA,U+02DC,U+0304,U+0308,U+0329,U+2000-206F,U+20AC,U+2122,U+2191,U+2193,U+2212,U+2215,U+FEFF,U+FFFD;}</style> <style id='page-skin-1' type='text/css'></style> <style id='template-skin-1' type='text/css'></style> <meta content='width=device-width, initial-scale=1.0, maximum-scale=12.0, minimum-scale=.25, user-scalable=yes' name='viewport'/> <meta content='mw8ww70r3jW0GzXY6j1d' name='follow_it-verification-code'/> <link href='https://www.blogger.com/dyn-css/authorization.css?targetBlogID=6264947694886887540&zx=ee9ac79c-a7e3-41c3-b260-c102f65f80e8' media='none' onload='if(media!='all')media='all'' rel='stylesheet'/><noscript><link href='https://www.blogger.com/dyn-css/authorization.css?targetBlogID=6264947694886887540&zx=ee9ac79c-a7e3-41c3-b260-c102f65f80e8' rel='stylesheet'/></noscript> <meta name='google-adsense-platform-account' content='ca-host-pub-1556223355139109'/> <meta name='google-adsense-platform-domain' content='blogspot.com'/> </head> <body class='loading'> <div class='navbar no-items section' id='navbar'> </div> <div class='body-fauxcolumns'> <div class='fauxcolumn-outer body-fauxcolumn-outer'> <div class='cap-top'> <div class='cap-left'></div> <div class='cap-right'></div> </div> <div class='fauxborder-left'> <div class='fauxborder-right'></div> <div class='fauxcolumn-inner'> </div> </div> <div class='cap-bottom'> <div class='cap-left'></div> <div class='cap-right'></div> </div> </div> </div> <div class='content'> <div class='content-fauxcolumns'> <div class='fauxcolumn-outer content-fauxcolumn-outer'> <div class='cap-top'> <div class='cap-left'></div> <div class='cap-right'></div> </div> <div class='fauxborder-left'> <div class='fauxborder-right'></div> <div class='fauxcolumn-inner'> </div> </div> <div class='cap-bottom'> <div class='cap-left'></div> <div class='cap-right'></div> </div> </div> </div> <div class='content-outer'> <div class='content-cap-top cap-top'> <div class='cap-left'></div> <div class='cap-right'></div> </div> <div class='fauxborder-left content-fauxborder-left'> <div class='fauxborder-right content-fauxborder-right'></div> <div class='content-inner'> <header> <div class='header-outer'> <div class='header-cap-top cap-top'> <div class='cap-left'></div> <div class='cap-right'></div> </div> <div class='fauxborder-left header-fauxborder-left'> <div class='fauxborder-right header-fauxborder-right'></div> <div class='region-inner header-inner'> <div class='header section' id='header'><div class='widget Header' data-version='1' id='Header1'> <div id='header-inner' style='background-image: url("https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi-4KXwYe0lQ4HFzhAye9vvRlij2ZYvMbfPCnqEE__1o85Fjo3XgefxJQhWRdwR3EzNWNMWT3yMaj2QZaT9GazqQx3C6oWa3-hBNlRHG7f-Oib-lv1Wq_C2_A0rt8xZgs87iNqzRVKK7H0A/s800/background.jpg"); background-position: left; width: 550px; min-height: 105px; _height: 105px; background-repeat: no-repeat; '> <div class='titlewrapper' style='background: transparent'> <h1 class='title' style='background: transparent; border-width: 0px'> <a href='http://www.righto.com/'> Ken Shirriff's blog </a> </h1> </div> <div class='descriptionwrapper'> <p class='description'><span>Computer history, restoring vintage computers, IC reverse engineering, and whatever</span></p> </div> </div> </div></div> </div> </div> <div class='header-cap-bottom cap-bottom'> <div class='cap-left'></div> <div class='cap-right'></div> </div> </div> </header> <div class='tabs-outer'> <div class='tabs-cap-top cap-top'> <div class='cap-left'></div> <div class='cap-right'></div> </div> <div class='fauxborder-left tabs-fauxborder-left'> <div class='fauxborder-right tabs-fauxborder-right'></div> <div class='region-inner tabs-inner'> <div class='tabs no-items section' id='crosscol'></div> <div class='tabs no-items section' id='crosscol-overflow'></div> </div> </div> <div class='tabs-cap-bottom cap-bottom'> <div class='cap-left'></div> <div class='cap-right'></div> </div> </div> <div class='main-outer'> <div class='main-cap-top cap-top'> <div class='cap-left'></div> <div class='cap-right'></div> </div> <div class='fauxborder-left main-fauxborder-left'> <div class='fauxborder-right main-fauxborder-right'></div> <div class='region-inner main-inner'> <div class='columns fauxcolumns'> <div class='fauxcolumn-outer fauxcolumn-center-outer'> <div class='cap-top'> <div class='cap-left'></div> <div class='cap-right'></div> </div> <div class='fauxborder-left'> <div class='fauxborder-right'></div> <div class='fauxcolumn-inner'> </div> </div> <div class='cap-bottom'> <div class='cap-left'></div> <div class='cap-right'></div> </div> </div> <div class='fauxcolumn-outer fauxcolumn-left-outer'> <div class='cap-top'> <div class='cap-left'></div> <div class='cap-right'></div> </div> <div class='fauxborder-left'> <div class='fauxborder-right'></div> <div class='fauxcolumn-inner'> </div> </div> <div class='cap-bottom'> <div class='cap-left'></div> <div class='cap-right'></div> </div> </div> <div class='fauxcolumn-outer fauxcolumn-right-outer'> <div class='cap-top'> <div class='cap-left'></div> <div class='cap-right'></div> </div> <div class='fauxborder-left'> <div class='fauxborder-right'></div> <div class='fauxcolumn-inner'> </div> </div> <div class='cap-bottom'> <div class='cap-left'></div> <div class='cap-right'></div> </div> </div>  <div class='columns-inner'> <div class='column-center-outer'> <div class='column-center-inner'> <div class='main section' id='main'><div class='widget Blog' data-version='1' id='Blog1'> <div class='blog-posts hfeed'> <div class="date-outer"> <div class="date-posts"> <div class='post-outer'> <div class='post hentry' itemprop='blogPost' itemscope='itemscope' itemtype='http://schema.org/BlogPosting'> <meta content='https://static.righto.com/images/ibm-360-50/screenshot-w450.jpg' itemprop='image_url'/> <meta content='6264947694886887540' itemprop='blogId'/> <meta content='1556663171519058512' itemprop='postId'/> <a name='1556663171519058512'></a> <h3 class='post-title entry-title' itemprop='name'> <a href='http://www.righto.com/2022/01/ibm360model50.html'>Simulating the IBM 360/50 mainframe from its microcode</a> </h3> <div class='post-header'> <div class='post-header-line-1'></div> </div> <div class='post-body entry-content' id='post-body-1556663171519058512' itemprop='description articleBody'> <style> .hilite {cursor:zoom-in} a:link img.hilite, a:visited img.hilite { color: #fff;} </style> <p>The IBM System/360 was a groundbreaking family of mainframe computers announced on April 7, 1964. System/360 was an extremely risky "bet-the-company" project for IBM, costing over $5 billion, but the System/360 ended up as a huge success, setting the direction of the computer industry for decades. The S/360 architecture was so successful that it is still supported by IBM's latest mainframes, almost 60 years later. I'm developing a microcode-level simulator<span id="fnref:simulator"><a class="ref" href="#fn:simulator">1</a></span> for the IBM System/360 Model 50 (<a href="http://righto.com/360">link to the simulator</a>); this blog post provides background to understand the Model 50 and the simulator.</p> <p><a href="https://righto.com/360"><img alt="Screenshot of the simulator running in a browser." class="hilite" height="387" src="https://static.righto.com/images/ibm-360-50/screenshot-w450.jpg" title="Screenshot of the simulator running in a browser." width="450" /></a><div class="cite">Screenshot of the simulator running in a browser.</div></p> <p>The radical decision behind System/360 was to use a single architecture for the entire product line of computers.<span id="fnref:variants"><a class="ref" href="#fn:variants">3</a></span> The name symbolized “360 degrees to cover the entire circle of possible uses.” Using a common architecture seems obvious now (e.g. x86), but prior to the System/360, IBM (like other computer manufacturers) produced multiple computers with entirely incompatible architectures.</p> <p>Internally, the different System/360 models had completely different implementations to support a wide range of cost and performance levels: the fastest model was over 1000 times as powerful as the slowest. Low-end models used simple hardware and an 8-bit datapath while advanced models used wide datapaths, fast semiconductor registers, out-of-order instruction execution, and caches.<span id="fnref:architectures"><a class="ref" href="#fn:architectures">2</a></span> Despite these internal differences, the models all looked the same to the programmer.</p> <style type="text/css"> .halfspace { margin-block-start: .5em; margin-block-end: .5em;} </style> <h2>Architecture of System/360<span id="fnref:princops"><a class="ref" href="#fn:princops">4</a></span></h2> <p>You might expect a computer architecture from the 1960s to be simple, but System/360 is remarkably complex, partly because it merged six computer families into one architecture.  It is a 32-bit architecture that supports many datatypes. As well as 32-bit integers and half words, it supports decimal arithmetic on numbers up to 31 digits long. Floating-point arithmetic supports short (32 bit), long (64 bit), or extended (128 bit) values. The processor also supports character strings up to 256 bytes long. </p> <p>The System/360 instruction set has about 100 different instructions and several addressing modes. Some of these instructions are straightforward arithmetic, logic, or control operations. Other instructions are more complex, such as the "character move" that copies up to 256 characters in memory, or the floating-point instructions.</p> <p>One of the most complex instructions is "edit", which formats a sequence of decimal digits for printing, for example inserting commas, a minus sign, or decimal point; removing leading zeroes, or filling leading spaces with characters. The number 1234567 could be "edited" into the string "$***12,345.67" for printing on a check. Keep in mind that this is a <em>single</em> instruction, not a library function like <code>printf</code>.</p>    <p><a href="https://static.righto.com/images/ibm-360-50/IBM_system_360-50_console_-_MfK_Bern.jpg"><img alt="IBM System/360 Model 50 control panel. The dataflow diagram in the upper right illustrates the system's internal design. Photo by Sandstein, CC BY-SA 3.0." class="hilite" height="476" src="https://static.righto.com/images/ibm-360-50/IBM_system_360-50_console_-_MfK_Bern-w400.jpg" title="IBM System/360 Model 50 control panel. The dataflow diagram in the upper right illustrates the system's internal design. Photo by Sandstein, CC BY-SA 3.0." width="400" /></a><div class="cite">IBM System/360 Model 50 control panel. The dataflow diagram in the upper right illustrates the system's internal design. Photo by <a href="https://commons.wikimedia.org/wiki/File:IBM_system_360-50_console_-_MfK_Bern.jpg">Sandstein</a>, <a href="https://creativecommons.org/licenses/by-sa/3.0/deed.en">CC BY-SA 3.0</a>.</div></p> <p>The System/360 architecture also included I/O, defining IBM's "channel" architecture. A channel is a programmable I/O subsystem with its own instruction set. On larger systems, the channel was an independent unit connected to the computer. But smaller systems such as the Model 50 used the same microcode engine to run CPU programs and channel programs.</p> <p>The point is that System/360 has a large and complex instruction set. A single instruction could result in hundreds of memory accesses and processing steps. The dense instruction set helped programmers to cram programs into the extremely limited core memory of the 1960s. However, the complex instruction set was a problem for the computer designer, who had to implement the complex circuitry to carry out these instructions. The solution was microcode.</p> <p><a href="https://static.righto.com/images/ibm-360-50/model-50-ibm.jpg"><img alt="The System/360 Model 50 in a datacenter. The console and processor are at the left. An IBM 1442 card reader/punch is behind the IBM 1052 printer-keyboard that the operator is using. At the back, another operator is loading a tape onto an IBM 2401 tape drive. Photo from IBM." class="hilite" height="396" src="https://static.righto.com/images/ibm-360-50/model-50-ibm-w500.jpg" title="The System/360 Model 50 in a datacenter. The console and processor are at the left. An IBM 1442 card reader/punch is behind the IBM 1052 printer-keyboard that the operator is using. At the back, another operator is loading a tape onto an IBM 2401 tape drive. Photo from IBM." width="500" /></a><div class="cite">The System/360 Model 50 in a datacenter. The console and processor are at the left. An IBM 1442 card reader/punch is behind the IBM 1052 printer-keyboard that the operator is using. At the back, another operator is loading a tape onto an IBM 2401 tape drive. Photo from IBM.</div></p> <h2>Microcode</h2> <p>One of the hardest parts of computer design is creating the control logic that tells each part of the processor how to carry out each instruction. In 1951, Maurice Wilkes came up with the idea of microcode: instead of building the control circuitry from complex logic gates, the control logic could be replaced with code (i. e. microcode) stored in a special memory called a control store. To execute an instruction, the computer internally executes several simpler microinstructions, specified by the microcode. Microcode turns the processor's control logic into a programming task instead of a logic design task.<span id="fnref:control"><a class="ref" href="#fn:control">5</a></span></p> <p>Microcode played a key role in the success of the System/360, helping IBM produce a line of computers with the same instruction set architecture but widely different implementations. It also allowed a processor to support different instruction sets; System/360 machines could be backward compatible with customers' older machines<span id="fnref:compatibility"><a class="ref" href="#fn:compatibility">6</a></span> so customers could keep their existing software. For these reasons, the System/360 computers used microcode unless there was a compelling reason not to.<span id="fnref:non-microcode"><a class="ref" href="#fn:non-microcode">7</a></span></p> <p>Another advantage of microcode is that it provides an easy way to fix design flaws and bugs in the field. Instead of modifying the hardware, a service engineer could replace the microcode with a new version. The photo below shows a copper sheet with microcode etched into it for the Model 50.</p> <p><a href="https://static.righto.com/images/ibm-360-50/model_50_CROS_plane.jpg"><img alt="A replaceable BCROS sheet, holding 17,600 bits. Dimensions are 505mm × 211mm. Photo courtesy of Chris Bigos." class="hilite" height="213" src="https://static.righto.com/images/ibm-360-50/model_50_CROS_plane-w500.jpg" title="A replaceable BCROS sheet, holding 17,600 bits. Dimensions are 505mm × 211mm. Photo courtesy of Chris Bigos." width="500" /></a><div class="cite">A replaceable BCROS sheet, holding 17,600 bits. Dimensions are 505mm × 211mm. Click for a high-resolution version. Photo courtesy of <a href="https://www.ibm360.info">Chris Bigos</a>.</div></p> <p>Microcode can be implemented in a variety of ways. Many computers use "vertical microcode", where a microcode instruction is similar to a machine instruction, just less complicated. The System/360 designs, on the other hand, used "horizontal microcode", with complex, wide instructions of up to 100 bits, depending on the model. These microinstructions were more like a collection of fields, each controlling low-level signals. This improved performance since multiple parts of the processor could be controlled in parallel. </p> <h2>Hardware of the Model 50<span id="fnref:refs"><a class="ref" href="#fn:refs">8</a></span></h2> <p>The Model 50 was roughly in the middle of the System/360 lineup, providing a powerful mainframe that could be used by a medium-sized business or university department. The Model 50 <a href="https://books.google.com/books?id=pFzxLUAnSS8C&lpg=PA88&dq=ibm%20360%20rental%20price%20%22model%2030%22%20-computerworld&pg=PA88#v=onepage&q=ibm%20360%20&f=false">typically</a> <a href="https://books.google.com/books?id=xLTiBQAAQBAJ&lpg=PA213&dq=ibm%20360%20rental%20price%20%22model%2050%22%20-computerworld&pg=PA213#v=onepage&q=%20%22model%2040%22%20&f=false">rented</a> for about $18,000 - $32,000 per month (equivalent to $120,000-$200,000 a month in current dollars).</p>  <p><a href="https://static.righto.com/images/ibm-360-50/ibm-360-50.png"><img alt="IBM S/360 Model 50. The console was attached to the main frame, about 5 feet deep. The storage frame and power frame are the black cabinets at the back. Photo from Pinterest." class="hilite" height="343" src="https://static.righto.com/images/ibm-360-50/ibm-360-50-w500.png" title="IBM S/360 Model 50. The console was attached to the main frame, about 5 feet deep. The storage frame and power frame are the black cabinets at the back. Photo from Pinterest." width="500" /></a><div class="cite">IBM S/360 Model 50. The console was attached to the main frame, about 5 feet deep. The storage frame and power frame are the black cabinets at the back. Photo from <a href="https://www.pinterest.com/pin/123145371033491049/">Pinterest</a>.</div></p> <p>The Model 50 occupied three large cabinets, each 5 feet long, about 2 feet wide, 6 feet tall, and weighing nearly a ton each.<span id="fnref:dimensions"><a class="ref" href="#fn:dimensions">9</a></span> The main frame, behind the console, contained the CPU, I/O channel circuitry, and the microcode storage. Behind this, the power cabinet contained the computer's power supplies. To the left, the cabinet at the back contained the main storage: one or two core memory modules, each with 128 kilobytes of memory. (I wrote in detail about the <a href="http://www.righto.com/2019/04/a-look-at-ibm-s360-core-memory-in-1960s.html">Model 50's core memory</a> earlier.) The computer's cables ran under a raised floor to the I/O devices, which typically included tape drives, a card reader, printers, disk drives, I/O controllers, and so forth.</p> <p><a href="https://static.righto.com/images/ibm-360-50/ibm-360-50-frames.png"><img alt="This diagram shows the three frames that made up the basic S/360 Model 50. Source: Model 50 Maintenance Manual page 138." class="hilite" height="326" src="https://static.righto.com/images/ibm-360-50/ibm-360-50-frames-w500.png" title="This diagram shows the three frames that made up the basic S/360 Model 50. Source: Model 50 Maintenance Manual page 138." width="500" /></a><div class="cite">This diagram shows the three frames that made up the basic S/360 Model 50. Source: <a href="http://www.bitsavers.org/pdf/ibm/360/fe/2050/SY22-2832-4_360-50Maint.pdf">Model 50 Maintenance Manual</a> page 138.</div></p> <p>The System/360 processors weren't implemented with integrated circuits, but with SLT (Solid Logic Technology) modules, hybrid modules that contain a few transistors, diodes, and resistors. A typical module implemented a logic gate, so it takes many circuit boards full of modules to construct the processor.</p> <p><a href="https://static.righto.com/images/ibm-360-50/logic-board.jpg"><img alt="A logic board using SLT modules. Each square metal can is a module." class="hilite" height="331" src="https://static.righto.com/images/ibm-360-50/logic-board-w300.jpg" title="A logic board using SLT modules. Each square metal can is a module." width="300" /></a><div class="cite">A logic board using SLT modules. Each square metal can is a module.</div></p> <p>Like most computers of the 1960s, the Model 50 used magnetic core memory, with a tiny ferrite ring to store each bit. The photo below shows a core plane that stores 32768 bits (along with 512 bits for I/O). A stack of 18 planes formed a 64-kilobyte memory module, with two parity bits.<span id="fnref:core"><a class="ref" href="#fn:core">10</a></span></p> <p><a href="https://static.righto.com/images/ibm-360-50/core-plane-50.jpg"><img alt="A Model 50 core plane is arranged as a grid of cores. The Y lines run horizontally. X and sense/inhibit lines run vertically. The sense/inhibit lines form loops at the top and bottom. Each of the four vertical pairs of blocks has separate sense/inhibit lines. Each core plane was about 10¾ × 6¾ × ⅛ inches." class="hilite" height="260" src="https://static.righto.com/images/ibm-360-50/core-plane-50-w500.jpg" title="A Model 50 core plane is arranged as a grid of cores. The Y lines run horizontally. X and sense/inhibit lines run vertically. The sense/inhibit lines form loops at the top and bottom. Each of the four vertical pairs of blocks has separate sense/inhibit lines. Each core plane was about 10¾ × 6¾ × ⅛ inches." width="500" /></a><div class="cite">A Model 50 core plane is arranged as a grid of cores. The Y lines run horizontally. X and sense/inhibit lines run vertically. The sense/inhibit lines form loops at the top and bottom. Each of the four vertical pairs of blocks has separate sense/inhibit lines. Each core plane was about 10¾ × 6¾ × ⅛ inches.</div></p> <h2>The Model 50's internal architecture</h2> <style type="text/css"> blockquote { margin: 25px auto; width: 60%; color: #555; padding: 5px 5px 1px 25px; border-left: 4px solid #ccc; background: #eee; position: relative;} blockquote p { font-style: italic; font-size: 120%; text-align: center; line-height: 150%;} blockquote:before {position: absolute; content: "\201C"; font-size: 4em; left: 3px; top: 7px; color: #ccc;} </style> <blockquote cite="http://www.bitsavers.org/pdf/ibm/360/fe/2040/SY22-2840-2_Model_40_Comprehensive_Introduction_Apr70.pdf"> <p> To the programmer, all processors within System/360 look the same; internal circuitry, however, may be entirely different. </p></blockquote> <p>It's important to keep in mind that the internal architecture of the Model 50 is very different from the architecture that the programmer sees.<span id="fnref:programmer"><a class="ref" href="#fn:programmer">11</a></span> In particular, the processor's internal registers are invisible to the programmer. The programmer instead sees 16 general-purpose registers and 4 floating-point registers, but to the processor these are part of the 64-word local store, a small high-speed core memory.</p> <p>The diagram below shows the complex data flow through the computer.<span id="fnref:dataflow"><a class="ref" href="#fn:dataflow">12</a></span> The black boxes are internal registers; the processor has a surprisingly large number of registers, used for a variety of purposes. The internal components are connected by buses. Most of the internal communication is over the 32-bit buses, shown in black. The 8-bit "mover" bus is shown in gray.</p> <p><a href="https://static.righto.com/images/ibm-360-50/diagram.jpg"><img alt="This diagram shows the data flow through the IBM 360/50 and appears in the upper-right corner of the console. I drew this version since I couldn't find a clear photo of it." class="hilite" height="434" src="https://static.righto.com/images/ibm-360-50/diagram-w900.jpg" title="This diagram shows the data flow through the IBM 360/50 and appears in the upper-right corner of the console. I drew this version since I couldn't find a clear photo of it." width="900" /></a><div class="cite">This diagram shows the data flow through the IBM 360/50 and appears in the upper-right corner of the console. I drew this version since I couldn't find a clear photo of it.</div></p> <p>The heart of the computer is the 32-bit adder, which performs addition. For subtraction, the argument is complemented by the True/Complement circuit (TC). The adder has an associated shifter to perform bit-shifts; this is especially important for multiplication, division, and floating-point calculations. Operating in parallel with the adder is the "mover", which operates on bytes. It can extract a byte from a 32-bit word, as well as manipulating 4-bit pieces of the byte. The mover also performs Boolean operations (AND, OR, XOR). (Unlike most processors, the Model 50 separates arithmetic and logical operations, instead of having an ALU perform both.)</p> <p>The computer's main core-memory storage is on the left. To access memory, an address is put in the Storage Address Register (SAR). Data is then read or written through the Storage Data Register (SDR). To the left of main storage, is the Instruction Address Register (the Program Counter or PC in modern terms). At the top is the Local Store, 64 words of high-speed core memory that holds the programmer's registers as well as some internal storage. The local store is accessed through the Local Store Address Register (LSAR).</p> <p>At the right are the I/O channels: the low-speed Multiplexor Channel and the high-speed Selector Channel. You can think of these as DMA (direct memory access) paths for I/O. The multiplexor channel communicates over an 8-bit bus through the mover, while the selector channel communicates over a 32-bit bus. Although the channels are conceptually separate from the processor, the channels use the same buses, circuitry, and microcode engine as the processor. This limits I/O performance compared to more advanced System/360 models that have independent circuitry for the channels.</p> <h2>An example of the microcode</h2> <p>As you can see, the processor has many registers and functional units. The microcode needs to control these components to carry out program instructions. The microcode architecture is very complex and takes over 100 pages to explain thoroughly,<span id="fnref:microcode-ref"><a class="ref" href="#fn:microcode-ref">15</a></span> so I'm only able to scratch the surface here. Each microinstruction is 90 bits long and performs multiple tasks. In the documentation, IBM used an 11-line block to represent each microinstruction, showing all the activities that are taking place in parallel.</p> <p>A sample microinstruction is shown below, part of the microcode that implements an add instruction. At this point, earlier microinstructions have fetched and decoded the instruction and put the arguments into the R and L registers. This microinstruction performs the actual 32-bit addition, but there's a lot more happening than just the addition.</p> <p><a href="https://static.righto.com/images/ibm-360-50/microcode-diagram.jpg"><img alt="One microinstruction, part of the integer addition code. This microinstruction is at micro-address 0220." class="hilite" height="354" src="https://static.righto.com/images/ibm-360-50/microcode-diagram-w500.jpg" title="One microinstruction, part of the integer addition code. This microinstruction is at micro-address 0220." width="500" /></a><div class="cite">One microinstruction, part of the integer addition code. This microinstruction is at micro-address 0220.</div></p> <p>Starting with the line "R+L→R" (red), this indicates that the ALU is taking inputs from registers R and L, and the result is going into the R register. In other words, the two arguments are added. The result R is stored into the desired programmer-visible register in local storage (blue). The processor registers FN and J select the address in local storage. Meanwhile, the <code>SETCRALG</code> line sets the Condition code register based on the sign (i.e. "algebraic" value) of the result, indicating if the result is positive, negative, or zero.</p> <p>The line "BC⩝C" indicates that signed overflow is detected and used as the carry flag<span id="fnref:carry"><a class="ref" href="#fn:carry">14</a></span> while CAR (yellow) indicates the microcode branches on this carry (overflow) value. Thus, the microcode will take one path if the addition was valid and a second error path if overflow occurred.  A microinstruction can "emit" an arbitrary 4-bit value (green) which can be used in a variety of ways. In this case, the binary value 1000 is emitted, fed into the W register, and then the M register, for use by the next microinstruction. As you can see, the CPU performs many activities in parallel for one microinstruction, which increases the computer's performance.</p> <p>All the activities of a microinstruction are encoded into a 90-bit word consisting of 28 fields.<span id="fnref:bitstream"><a class="ref" href="#fn:bitstream">13</a></span> The microinstruction discussed above (micro-address 0220) is highlighted in the documentation below. A single microinstruction is very complex, which is why it takes an 11-line block of text to represent it.</p> <p><a href="https://static.righto.com/images/ibm-360-50/bitstream.jpg"><img alt="Part of the microcode listing. The previously-discussed microinstruction is highlighted. Note that the micro-address 0220 matches the address in the upper-left corner of the microinstruction diagram." class="hilite" height="101" src="https://static.righto.com/images/ibm-360-50/bitstream-w800.jpg" title="Part of the microcode listing. The previously-discussed microinstruction is highlighted. Note that the micro-address 0220 matches the address in the upper-left corner of the microinstruction diagram." width="800" /></a><div class="cite">Part of the <a href="http://www.bitsavers.org/pdf/ibm/360/fe/2050/2050_Vol20_Sep72.pdf">microcode listing</a>. The previously-discussed microinstruction is highlighted. Note that the micro-address 0220 matches the address in the upper-left corner of the microinstruction diagram.</div></p> <p>The processor documentation contains hundreds of pages of microcode;<span id="fnref:listing"><a class="ref" href="#fn:listing">16</a></span> one page of the floating-point multiply code is below. Each box is one microinstruction, and the lines between them indicate the complex control paths. I'm not going to explain this microcode,<span id="fnref:explanation"><a class="ref" href="#fn:explanation">17</a></span> but I wanted to show its complexity.</p> <p><a href="https://static.righto.com/images/ibm-360-50/fp-microcode.jpg"><img alt="Part of the floating-point multiply microcode. (Click for a larger view.) From ALD vol 18." class="hilite" height="452" src="https://static.righto.com/images/ibm-360-50/fp-microcode-w700.jpg" title="Part of the floating-point multiply microcode. (Click for a larger view.) From ALD vol 18." width="700" /></a><div class="cite">Part of the floating-point multiply microcode. (Click for a larger view.) From <a href="http://www.bitsavers.org/pdf/ibm/360/fe/2050/2050_Vol18_Sep72.pdf">ALD vol 18</a>.</div></p> <h2>The console</h2> <p>The discussion above has shown the complex internal architecture of the Model 50. The numerous lights and controls on the console<span id="fnref:console"><a class="ref" href="#fn:console">19</a></span> provide a view into this internal state. There were three main uses for the console. The first use was basic "operator control" tasks such as turning the system on, booting it, or powering it off, using the controls in the lower section of the console. These controls were consistent across the S/360 line and were usually the only controls the operator needed. The three hexadecimal dials in the lower right selected the I/O unit that held the boot software. Once the system had booted, the operator generally typed commands into the system rather than using the console.</p> <p><a href="https://static.righto.com/images/ibm-360-50/ibm-360-50-marc.jpg"><img alt="Control panel of the IBM System/360 Model 50. This panel has marginal check controls for auxiliary storage in the upper right, replacing the dataflow diagram." class="hilite" height="613" src="https://static.righto.com/images/ibm-360-50/ibm-360-50-marc-w450.jpg" title="Control panel of the IBM System/360 Model 50. This panel has marginal check controls for auxiliary storage in the upper right, replacing the dataflow diagram." width="450" /></a><div class="cite">Control panel of the IBM System/360 Model 50. This panel has marginal check controls for auxiliary storage in the upper right, replacing the dataflow diagram.</div></p> <p>The second console function was "operator intervention": program debugging tasks such as examining and modifying memory or registers and setting breakpoints. The lights and toggle switches in the lower half of the console were used for operator intervention. The operator could enter a 24-bit address using the row of 24 toggle switches, and enter a 32-bit data value using the row of 32 toggle switches above. The lights allowed the contents of memory to be examined. With other switches, the operator could set a breakpoint, single-step through a program, and perform other debugging operations.</p> <p>The third console function was system maintenance and repair performed by an IBM customer engineer. The customer engineering displays took up the top half of the console and provided detailed access to the computer's complex internal state. To save space, the Model 50 had four roller knobs on the right side, with 8 positions for each knob. Each knob position selected a different function for the row of 36 lights (32 bits plus parity). The legends above the lights rotate with the knobs, showing the meaning of each light. For example, one position would display the L register, while another position would display the current microinstruction. In the photo below, the upper roller and lights are displaying part of the microcode currently being executed (ROS = Read Only Store). The roller below shows some of the internal registers and counters.</p> <p><a href="https://static.righto.com/images/ibm-360-50/rollers.jpg"><img alt="Closeup of two rollers and the associated lights." class="hilite" height="215" src="https://static.righto.com/images/ibm-360-50/rollers-w500.jpg" title="Closeup of two rollers and the associated lights." width="500" /></a><div class="cite">Closeup of two rollers and the associated lights.</div></p> <p>Finally, the voltmeter and voltage control knobs in the upper left of the console were used by an IBM customer engineer for "marginal checking". By raising and lowering the voltage levels, borderline components could be detected and replaced before they caused problems.</p> <h2>The simulator</h2> <p>The simulator is at <a href="http://righto.com/360">righto.com/360</a> and the code is on <a href="https://github.com/shirriff/ibm-system-360-50-simulator">Github</a>. I implemented the simulator in JavaScript so it can run in a browser. It runs a sample program by executing the Model 50's microcode, simulating each microinstruction and the hardware. Each microinstruction is displayed graphically, along with the current instruction, the registers, the local storage, and core memory. It displays the console lights accurately based on the internal state, on a zoomable virtual console. Each row of lights can display 8 different elements, which you can change by clicking on a roller. You can step also through the microcode, one microinstruction at a time.</p> <p>This simulator is still under development so don't expect it to work perfectly. I also haven't implemented the toggle switches, so you can't enter a program from the console yet. I also need to implement the I/O system, which has its own registers and a different microcode format.</p> <p>To build the simulator, I extracted the binary microcode from the <a href="http://www.bitsavers.org/pdf/ibm/360/fe/2050/2050_Vol20_Sep72.pdf">listings</a> using a custom OCR tool. I implemented the hundreds of micro-operations, which were tricky to get correct. While most micro-operations are simple operations such as moving a register to the bus, some microinstructions are much more complex, especially for floating-point operations.<span id="fnref:edfp"><a class="ref" href="#fn:edfp">20</a></span> Another complication is that a microinstruction performs many tasks in parallel and it was hard to determine the exact order in which to perform them. </p> <p>My eventual goal with the simulator is to move it into the physical world. Specifically, I plan to drive the lights on CuriousMarc's <a href="https://www.youtube.com/watch?v=WS-WtjwAAO0">Model 50 control panel</a> to make the panel operate accurately. We also plan to hook up his IBM tape drives and card reader so we can have all the pieces of a Model 50 mainframe working together, except for the processor itself. I plan to port the simulator to C so I can run it in a microcontroller to drive the physical console. An FPGA implementation is another possibility; this would provide the maximum speed, but would be harder to implement.</p> <p>I announce my latest blog posts on Twitter, so follow me <a href="https://twitter.com/kenshirriff">@kenshirriff</a> for updates and future articles. I also have an <a href="http://www.righto.com/feeds/posts/default">RSS feed</a>. Thanks to Richard Cornwell for discussion and data.</p> <h2>Notes and references</h2> <div class="footnote"> <ol> <li id="fn:simulator"> <p>My simulator is not particularly useful unless you really care about the microcode in the Model 50. If you want to run software on a simulated System/360, you probably want to use the <a href="http://www.hercules-390.eu/">Hercules system</a>. <a class="footnote-backref" href="#fnref:simulator" title="Jump back to footnote 1 in the text">↩</a></p> </li> <li id="fn:architectures"> <p>I'll briefly summarize some of the different implementations used in System/360 computers. <p class="halfspace"/>The low-end Model 30 uses an 8-bit bus and ALU, so 32-bit operations take four steps. It uses 60-bit microcode. <p class="halfspace"/>The Model 40 also has an 8-bit bus and ALU, but it has 16-bit registers and a 16-bit bus to memory, improving the performance. It has 60-bit microcode. <p class="halfspace"/>The Model 50 (discussed in this blog post) has 32-bit registers, memory bus, and adder. It also has the 8-bit mover that can operate in parallel with the adder. <p class="halfspace"/>The Model 65 has a 64-bit bus, and multiple adders (60 and 8-bit) that allow a floating-point fraction and exponent to be processed in parallel. It also has an 8-byte instruction buffer and external channels. It uses 100-bit microcode. <p class="halfspace"/>The Model 75 has a 64-bit main adder, 8-bit exponent adder, 8-bit decimal adder, and a 24-bit addressing adder. It overlaps instruction fetching and execution, with 16 bytes of instruction prefetching and 8 bytes of data prefetching. <p class="halfspace"/>The high-end Model 91 has an advanced superscalar architecture with out-of-order execution, instruction pipelining, and multiple arithmetic execution units. Higher models support memory interleaving for faster access: 2-way on the Model 65 up to 16-way on the Model 195. <p class="halfspace"/>The models 44, 75, 91 and above used hardwired control instead of microcode to squeeze out more performance. <p class="halfspace"/> As you can see, the System/360 line has a wide variety of implementations. At the low end, the hardware is kept to a minimum to reduce costs, while at the high end, more hardware boosts performance, with wider datapaths and multiple functional units providing parallelism. <a class="footnote-backref" href="#fnref:architectures" title="Jump back to footnote 2 in the text">↩</a></p> </li> <li id="fn:variants"> <p>The System/360 line didn't completely meet the goal of a compatible architecture. IBM split out the business and scientific markets on the low-end machines by marketing subsets of the instruction set. The basic instructions were provided in the "standard" instruction set. On top of this, decimal instructions (for business) were in the "commercial" instruction set and floating-point was in the "scientific" instruction set. The "universal" instruction set provided all these instructions plus storage protection (i.e. memory protection between programs). Additionally, cost-cutting on the low-end Model 20 made it incompatible with the S/360 architecture, and the Model 44 was somewhat incompatible to improve performance on scientific applications. <a class="footnote-backref" href="#fnref:variants" title="Jump back to footnote 3 in the text">↩</a></p> </li> <li id="fn:princops"> <p>IBM defined the System/360 architecture in great detail in a document called the <a href="http://bitsavers.trailing-edge.com/pdf/ibm/360/princOps/A22-6821-0_360PrincOps.pdf">IBM System/360 Principles of Operation</a>. It describes not only the instruction set, but also the datatypes, input/output model, the interrupt model, and even the basic structure of the system control panel. To learn more about System/360, see <a href="http://www.bitsavers.org/pdf/ibm/360/training/C20-1646-1_A_Programmers_Introduction_To_IBM_System360_Assembler_Language_May66.pdf">A Programmer's Introduction to the IBM System/360 Architecture, Instructions, and Assembler Language</a>. A bunch of assembly examples are at <a href="https://rosettacode.org/wiki/Category:360_Assembly">rosettacode</a>. <a class="footnote-backref" href="#fnref:princops" title="Jump back to footnote 4 in the text">↩</a></p> </li> <li id="fn:control"> <p>The primary benefit of microcode for IBM was economic. As described in <a href="https://doi.org/10.1147/sj.64.0222">Microprogram Control for System/360</a>, the cost of a non-microcoded processor is roughly linear in the size of the instruction set. However, a microcoded system has a roughly fixed cost, with a small overhead for additional instructions. Thus, as instruction sets get more complex (as in System/360), there is a crossover point where microcode is more efficient. This is especially the case for smaller systems where the base cost is lower. The lower marginal cost also makes emulating other systems more feasible. The IBM System/360 was one of the first commercial computers to make extensive use of microcode. <a class="footnote-backref" href="#fnref:control" title="Jump back to footnote 5 in the text">↩</a></p> </li> <li id="fn:compatibility"> <p>Various System/360 machines supported compatibility features with earlier IBM computers including the 1401, 1440, 1620, 7070, 7074, 7080, 709, 7090, 7094. Generally, a smaller System/360 machine could replace a smaller IBM computer such as the 1401, while a larger mainframe such as the 7090 needed to be replaced by a larger System/360 computer such as the Model 65.  <a class="footnote-backref" href="#fnref:compatibility" title="Jump back to footnote 6 in the text">↩</a></p> </li> <li id="fn:non-microcode"> <p>A few System/360 models did not use microcode. The Model 44 was designed as a high-performance computer for scientific applications, so it used hardwired control. The Model 85 was partially microcoded, while the Models 75 and 91 were completely hardwired. <a class="footnote-backref" href="#fnref:non-microcode" title="Jump back to footnote 7 in the text">↩</a></p> </li> <li id="fn:refs"> <p>The book <a href="https://amzn.to/2E7ZxqP">IBM's 360 and Early 370 Systems</a> describes the history of the S/360 in great detail. IBM lists <a href="https://www.ibm.com/ibm/history/exhibits/mainframe/mainframe_FS360.html">data</a> on each model, including dates, data flow width, cycle time, storage, and microcode size. Another list with model details is <a href="https://www.ece.ucdavis.edu/~vojin/CLASSES/EEC272/S2005/Papers/Padegs-IBM360-sep81.pdf">here</a>. The article <a href="http://www.ece.ucdavis.edu/~vojin/CLASSES/EEC272/S2005/Papers/Padegs-IBM360-sep81.pdf">System/360 and Beyond</a> has lots of info. A list of 360 models and brief descriptions is <a href="http://www.beagle-ears.com/lars/engineer/comphist/model360.htm">here</a>. For information on the Model 50 specifically, see the <a href="http://www.bitsavers.org/pdf/ibm/360/funcChar/A22-6898-1_360-50_funcChar_1967.pdf">Functional Characteristics</a> manual, <a href="http://bitsavers.org/pdf/ibm/360/fe/2050/">Field Engineering</a> manuals, <a href="https://en.wikipedia.org/wiki/IBM_System/360_Model_50">Wikipedia</a>, photos <a href="http://infolab.stanford.edu/pub/voy/museum/pictures/display/3-1.htm">here</a> and <a href="https://commons.wikimedia.org/wiki/File:ERMETH_input.jpg">here</a>, <a href="https://www.youtube.com/watch?v=WS-WtjwAAO0">CuriousMarc video</a>. <a class="footnote-backref" href="#fnref:refs" title="Jump back to footnote 8 in the text">↩</a></p> </li> <li id="fn:dimensions"> <p>For detailed dimensions of the System/360 components, see the <a href="http://www.bitsavers.org/pdf/ibm/360/fe/GC22-6820-12_System_360_Installation_Manual_Physical_Planning.pdf">Physical Planning Manual</a> For more memory, another 1500-pound frame could be added to the Model 50, boosting it from 256 kilobytes of memory to 512 kilobytes. Up to four Large Capacity Storage units (IBM 2361) could be added, each providing two more megabytes. <a class="footnote-backref" href="#fnref:dimensions" title="Jump back to footnote 9 in the text">↩</a></p> </li> <li id="fn:core"> <p>I wrote in detail about the Model 50's core memory system <a href="http://www.righto.com/2019/04/a-look-at-ibm-s360-core-memory-in-1960s.html">here</a>. <a class="footnote-backref" href="#fnref:core" title="Jump back to footnote 10 in the text">↩</a></p> </li> <li id="fn:programmer"> <p>The quote is from System/360 Model 40 <a href="http://www.bitsavers.org/pdf/ibm/360/fe/2040/SY22-2840-2_Model_40_Comprehensive_Introduction_Apr70.pdf">comprehensive introduction</a>. <a class="footnote-backref" href="#fnref:programmer" title="Jump back to footnote 11 in the text">↩</a></p> </li> <li id="fn:dataflow"> <p>The Model 50 <a href="http://www.bitsavers.org/pdf/ibm/360/fe/2050/Z22-2833-R_2050_Processing_Unit_Field_Engineering_Diagram_Manual_Jul66.pdf">Field Engineering Diagram Manual</a> contains the detailed data flow diagram below. This diagram corresponds to the diagram discussed earlier, but provides much more detail. In particular, it shows the exact bit widths of the various data paths and registers.</p> <p><a href="https://static.righto.com/images/ibm-360-50/data-flow.png"><img alt="The detailed data flow diagram. Click for a larger version." class="hilite" height="620" src="https://static.righto.com/images/ibm-360-50/data-flow-w800.png" title="The detailed data flow diagram. Click for a larger version." width="800" /></a><div class="cite">The detailed data flow diagram. Click for a larger version.</div></p> <p> <a class="footnote-backref" href="#fnref:dataflow" title="Jump back to footnote 12 in the text">↩</a></p> </li> <li id="fn:bitstream"> <p><style type="text/css"> table.sim50 {border-collapse: collapse; font-size: 85%;} .sim50 th {border-bottom: 1px solid #ccc;} .sim50 td {padding-left: 10px; padding-right: 10px;} .sim50 td.hilite {background-color: #ffffcc;} .sim50 th:first-child {border-right: 1px solid #ccc;} .sim50 td:first-child {border-right: 1px solid #ccc; text-align: right;} </style></p> <p>The table below shows how a microinstruction is encoded into a 90-bit word.</p> <p><table class="sim50"> <tr><th>Bits</th><th>Name</th><th>Meaning</th></tr> <tr><td>0</td><td>P</td><td>Parity</td></tr> <tr><td>1-3</td><td>LU</td><td>Mover input left side</td></tr> <tr><td>4-5</td><td>MV</td><td>Mover input right side</td></tr> <tr><td>6-11</td><td>ZP</td><td>ROAR address (Read Only storage Address Register)</td></tr> <tr><td>12-15</td><td>ZF</td><td>ROAR branch control</td></tr> <tr><td>16-18</td><td>ZN</td><td>Address control field</td></tr> <tr><td>19-23</td><td>TR</td><td>Adder control</td></tr> <tr><td>24</td><td></td><td>Unused</td></tr> <tr><td>25-27</td><td>WS</td><td>Local store address control</td></tr> <tr><td>28-30</td><td>SF</td><td>Local store functions</td></tr> <tr><td>31</td><td>P</td><td>Parity</td></tr> <tr><td>32-34</td><td>IV</td><td>Invalid digit test</td></tr> <tr><td>35-39</td><td>AL</td><td>Adder latch gating</td></tr> <tr><td>40-43</td><td>WM</td><td>Mover destination</td></tr> <tr><td>44-45</td><td>UP</td><td>Byte counter function</td></tr> <tr><td>46</td><td>MD</td><td>MD counter control</td></tr> <tr><td>47</td><td>LB</td><td>L byte counter control</td></tr> <tr><td>48</td><td>MB</td><td>M byte counter control</td></tr> <tr><td>49-51</td><td>DG</td><td>Length counter</td></tr> <tr><td>52-53</td><td>UL</td><td>Mover function left digit</td></tr> <tr><td>54-55</td><td>UR</td><td>Mover function right digit</td></tr> <tr><td>56</td><td>P</td><td>Parity</td></tr> <tr><td>57-60</td><td>CE</td><td>Emit field</td></tr> <tr><td>61-63</td><td>LX</td><td>Left adder input</td></tr> <tr><td>64</td><td>TC</td><td>True or complement control</td></tr> <tr><td>65-67</td><td>RY</td><td>Right adder input</td></tr> <tr><td>68-71</td><td>AD</td><td>Adder function control</td></tr> <tr><td>72-77</td><td>AB</td><td>A branch control</td></tr> <tr><td>78-82</td><td>BB</td><td>B branch control</td></tr> <tr><td>83</td><td></td><td>Unused</td></tr> <tr><td>84-89</td><td>SS</td><td>Stat setting control</td></tr> </table></p> <p>For channel instructions, the microcode format is slightly different since some of the fields need to control the channel circuitry. However, most of the fields are the same as for the CPU. The table below shows the microcode format for the channel; the highlighted entries are different from the CPU microcode.</p> <p><table class="sim50"> <tr><th>Bits</th><th>Name</th><th>Meaning</th></tr> <tr><td>0</td><td>P</td><td>Parity</td></tr> <tr><td>1-3</td><td>LU</td><td>Mover input left side</td></tr> <tr><td>4-5</td><td>MV</td><td>Mover input right side</td></tr> <tr><td>6-11</td><td>ZP</td><td>ROAR address</td></tr> <tr><td>12-15</td><td>ZF</td><td>ROAR branch control</td></tr> <tr><td>16-18</td><td>ZN</td><td>Address control field</td></tr> <tr><td>19-23</td><td>TR</td><td>Adder control</td></tr> <tr><td>24</td><td></td><td>Unused</td></tr> <tr><td class="hilite">25</td><td>CS</td><td>Local storage address selector</td></tr> <tr><td class="hilite">26-27</td><td>SA</td><td>Local storage address</td></tr> <tr><td>28-30</td><td>SF</td><td>Local storage function</td></tr> <tr><td>31</td><td>P</td><td>Parity</td></tr> <tr><td class="hilite">32-34</td><td>CT</td><td>Timing signals to channel</td></tr> <tr><td>35-39</td><td>AL</td><td>Adder latch gating</td></tr> <tr><td class="hilite">40-42</td><td>WL</td><td>Mover destination</td></tr> <tr><td>43-46</td><td>HC</td><td>Multiplexor channel stat setting</td></tr> <tr><td class="hilite">47-48</td><td>CG</td><td>Control signals to channel</td></tr> <tr><td class="hilite">49-51</td><td>MG</td><td>Multiplexor channel gate control</td></tr> <tr><td>52-53</td><td>UL</td><td>Mover function left digit</td></tr> <tr><td>54-55</td><td>UR</td><td>Mover function right digit</td></tr> <tr><td>56</td><td>P</td><td>Parity</td></tr> <tr><td>57-60</td><td>CE</td><td>Emit field</td></tr> <tr><td>61-63</td><td>LX</td><td>Left adder input</td></tr> <tr><td>64</td><td>TC</td><td>True or complement control</td></tr> <tr><td>65-67</td><td>RY</td><td>Right adder input</td></tr> <tr><td class="hilite">68-70</td><td>CL</td><td>Selector channel adder latch tests</td></tr> <tr><td>71</td><td></td><td>Unused</td></tr> <tr><td>72-77</td><td>AB</td><td>A branch control</td></tr> <tr><td>78-82</td><td>BB</td><td>B branch control</td></tr> <tr><td>83</td><td></td><td>Unused</td></tr> <tr><td>84-89</td><td>SS</td><td>Stat setting control</td></tr> </table> <a class="footnote-backref" href="#fnref:bitstream" title="Jump back to footnote 13 in the text">↩</a></p> </li> <li id="fn:carry"> <p>When adding twos-complement signed numbers, an overflow occurs if the carry out of the most significant bit is different from the carry out of the second-most-significant bit. (I explain this in detail <a href="http://www.righto.com/2012/12/the-6502-overflow-flag-explained.html">here</a>.) IBM numbers the bits in a word "backward" with bit 0 the most significant. Thus, an overflow occurs if the carry from bit 0 XOR'd with the carry from bit 1 is nonzero. IBM uses ⩝ to indicate an exclusive or. Thus, CARRY(0) ⩝ CARRY(1) indicates an overflow, represented as BC⩝C in the microcode. <a class="footnote-backref" href="#fnref:carry" title="Jump back to footnote 14 in the text">↩</a></p> </li> <li id="fn:microcode-ref"> <p>For a description of how the Model 50 microcode works, see the book "Microprogramming: Principles and Practices", S. Husson (1970), pages 295 to 411. Bitsavers has a lot of <a href="http://www.bitsavers.org/pdf/ibm/360/fe/2050/">Model 50 documents</a>, but not everything. If you have additional documentation, such as the IBM Automated Logic Diagrams, please let me know. <a class="footnote-backref" href="#fnref:microcode-ref" title="Jump back to footnote 15 in the text">↩</a></p> </li> <li id="fn:listing"> <p>The Model 50's microcode listing is available in three volumes on <a href="http://bitsavers.org/pdf/ibm/360/fe/2050/2050_Vol20_Sep72.pdf">bitsavers</a>. The binary microcode listings are difficult to read with OCR because pages were printed on different printers; some use serif fonts and others use sans-serif fonts. I made my own OCR program designed to process binary, which was able to read the listings for the most part. The presence of parity in the microcode helped catch errors. <a class="footnote-backref" href="#fnref:listing" title="Jump back to footnote 16 in the text">↩</a></p> </li> <li id="fn:explanation"> <p>Ok, I'll give a brief explanation of that page of microcode, which is part of the implementation of floating-point multiplication. The implementation is designed with tradeoffs between speed, code length, and temporary memory usage. The idea is to multiply the multiplicand by the multiplier, kind of like long multiplication on paper, where you multiply a digit at a time and add the partial sums. This code processes a hex digit of the multiplier at a time, with a separate case for each digit. The multiplicand is multiplied by the digit and this is added to the running total, shifting as appropriate. To make this fast, multiples of the multiplicand are pre-computed. However, pre-computing 16 multiples (one for each hex digit value) would take too much temporary (local) storage. So the only pre-computed multiples are 1, 2, and 6, and these are combined for other digits. To multiply by the digit 7, for instance, the multiples for 1 and 6 are added. To multiply by the digit 4, the multiple for 6 is added and the multiple for 2 is subtracted. </p> <p>But what about multiplying by 9 through 15? The trick is to "borrow" 16 from the next-higher digit. For instance, to multiply by the digit 11, you borrow 16, subtract the multiple for 6, and add the multiple for 1. Then the value one less is used for the next digit to account for the borrow. Thus, all 16 possibilities can be handled by adding or subtracting at most two of the pre-computed values. With borrowing, the code needs to handle 32 cases; the included page implements 22 of these cases. This implementation makes multiplication rapid, but the microcode is complex with many paths. (There is also a bunch more code to handle the floating-point exponent, normalizing values, overflow, underflow, and so forth.) <a class="footnote-backref" href="#fnref:explanation" title="Jump back to footnote 17 in the text">↩</a></p> </li> <li id="fn:ros"> <p>Different System/360 models used a variety of methods to store microcode.<span id="fnref:ros"><a class="ref" href="#fn:ros">18</a></span> An important feature of IBM's microcode storage was that the microcode could be replaced in the field. The low-end Model 25 held microcode in a 16-kilobyte section of core memory called Control Storage. The Model 30 used CCROS (Card Capacitor Read-only Store), storing the microcode on special metalized punch cards that were read capacitively. Transformer Read-Only Storage (TROS, below) was used by the System/360 Model 20 and Model 40. I wrote an article about <a href="http://www.righto.com/2019/11/tros-how-ibm-mainframes-stored.html">microcode storage</a> if you want more information.</p> <p><a href="https://static.righto.com/images/ibm-360-50/tros.jpg"><img alt="A TROS module from an IBM System/360 Model 20." class="hilite" height="208" src="https://static.righto.com/images/ibm-360-50/tros-w500.jpg" title="A TROS module from an IBM System/360 Model 20." width="500" /></a><div class="cite">A TROS module from an IBM System/360 Model 20.</div></p>  <p>The Model 50 (as well as 65 and 67) stored microcode in BCROS (Balanced Capacitor Read-Only Storage), using copper-clad epoxy glass laminate boards, each 20″×8½″. Each sheet plane held 176 words of 100 bits, and the Model 50 used 16 sheets to store 2816 words. (Only 90 of the 100 bits in each word were used.) The data in BCROS was etched into the copper wiring (below).  Each bit is represented by two squares: one connected to the upper wire and one connected to the lower wire (or vice versa), forming the balanced capacitors.</p> <p><a href="https://static.righto.com/images/ibm-360-50/bcros-detail.jpg"><img alt="Closeup of a BCROS sheet from a System/360 Model 50." class="hilite" height="294" src="https://static.righto.com/images/ibm-360-50/bcros-detail-w300.jpg" title="Closeup of a BCROS sheet from a System/360 Model 50." width="300" /></a><div class="cite">Closeup of a BCROS sheet from a System/360 Model 50.</div></p> <p> <a class="footnote-backref" href="#fnref:ros" title="Jump back to footnote 18 in the text">↩</a></p> </li> <li id="fn:console"> <p>The features of the system control panel were carefully defined in the <a href="http://bitsavers.trailing-edge.com/pdf/ibm/360/princOps/A22-6821-0_360PrincOps.pdf">System/360 Principles of Operation</a> pages 117-121, providing a consistent operator experience across the S/360 line. (The customer engineering part of the panel, on the other hand, was not specified and wildly different across the product line.) Diagrams of S/360 consoles are at <a href="http://www.quadibloc.com/comp/pan04.htm">quadibloc</a>. For more details on the consoles, see my article on <a href="http://www.righto.com/2019/04/iconic-consoles-of-ibm-system360.html">System/360 consoles</a>. <a class="footnote-backref" href="#fnref:console" title="Jump back to footnote 19 in the text">↩</a></p> </li> <li id="fn:edfp"> <p>The micro-operation that caused me the most difficulty is ED*FP, which computes the difference between two exponents for floating-point, but also computes four floating-point flags including the sign depending on the type of operation. Not only is this operation complex, but I think there is a typo in the description.</p> <p><a href="https://static.righto.com/images/ibm-360-50/edfp.png"><img alt="A description of the ED*FP micro-operation." class="hilite" height="273" src="https://static.righto.com/images/ibm-360-50/edfp-w400.png" title="A description of the ED*FP micro-operation." width="400" /></a><div class="cite">A description of the ED*FP micro-operation.</div></p>  <p>Another complex micro-operation is <code>MLJK</code>, which performs multiple actions as part of instruction decoding:</p> <p>Gate adder latch to L reg and M reg. Gate latch bits 12-15 to J reg. Gate latch bits 16-19 to MD counter. Turn off refetch stat. <br/> If latch bits 12-15 all zero, turn on stat 0. Otherwise turn off stat 0. <br/> If latch bits 16-19 all zero, turn on stat 1. Otherwise turn off stat 1. <br/> If latch bits 16-17 all zero, turn on one-syllable stat. Otherwise turn off one-syllable stat. <br/> If latch bits 0-1 equal 00, set ILC to 01. <br/> If latch bits 0-1 equal 01 or 10, set ILC to 10. <br/> If latch bits 0-1 equal 11, set ILC to 11. <a class="footnote-backref" href="#fnref:edfp" title="Jump back to footnote 20 in the text">↩</a></p> </li> </ol> </div> <div style='clear: both;'></div> </div> <div class='post-footer'> <div class='post-footer-line post-footer-line-1'><span class='post-comment-link'> <a class='comment-link' href='https://www.blogger.com/comment/fullpage/post/6264947694886887540/1556663171519058512' onclick=''> 27 comments: </a> </span> <span class='post-icons'> <span class='item-action'> <a href='https://www.blogger.com/email-post/6264947694886887540/1556663171519058512' title='Email Post'> <img alt='' class='icon-action' height='13' src='http://img1.blogblog.com/img/icon18_email.gif' width='18'/> </a> </span> <span class='item-control blog-admin pid-1138732533'> <a href='https://www.blogger.com/post-edit.g?blogID=6264947694886887540&postID=1556663171519058512&from=pencil' title='Edit Post'> <img alt='' class='icon-action' height='18' src='https://resources.blogblog.com/img/icon18_edit_allbkg.gif' width='18'/> </a> </span> </span> <span class='post-backlinks post-comment-link'> </span> <div class='post-share-buttons goog-inline-block'> <a class='goog-inline-block share-button sb-email' href='https://www.blogger.com/share-post.g?blogID=6264947694886887540&postID=1556663171519058512&target=email' target='_blank' title='Email This'><span class='share-button-link-text'>Email This</span></a><a class='goog-inline-block share-button sb-blog' href='https://www.blogger.com/share-post.g?blogID=6264947694886887540&postID=1556663171519058512&target=blog' onclick='window.open(this.href, "_blank", "height=270,width=475"); return false;' target='_blank' title='BlogThis!'><span class='share-button-link-text'>BlogThis!</span></a><a class='goog-inline-block share-button sb-twitter' href='https://www.blogger.com/share-post.g?blogID=6264947694886887540&postID=1556663171519058512&target=twitter' target='_blank' title='Share to X'><span class='share-button-link-text'>Share to X</span></a><a class='goog-inline-block share-button sb-facebook' href='https://www.blogger.com/share-post.g?blogID=6264947694886887540&postID=1556663171519058512&target=facebook' onclick='window.open(this.href, "_blank", "height=430,width=640"); return false;' target='_blank' title='Share to Facebook'><span class='share-button-link-text'>Share to Facebook</span></a><a class='goog-inline-block share-button sb-pinterest' href='https://www.blogger.com/share-post.g?blogID=6264947694886887540&postID=1556663171519058512&target=pinterest' target='_blank' title='Share to Pinterest'><span class='share-button-link-text'>Share to Pinterest</span></a> </div> </div> <div class='post-footer-line post-footer-line-2'><span class='post-labels'> Labels: <a href='http://www.righto.com/search/label/ibm' rel='tag'>ibm</a>, <a href='http://www.righto.com/search/label/ibm360' rel='tag'>ibm360</a>, <a href='http://www.righto.com/search/label/microcode' rel='tag'>microcode</a>, <a href='http://www.righto.com/search/label/reverse-engineering' rel='tag'>reverse-engineering</a> </span> </div> <div class='post-footer-line post-footer-line-3'></div> </div> </div> </div> </div></div> <div class="date-outer"> <div class="date-posts"> <div class='post-outer'> <div class='post hentry' itemprop='blogPost' itemscope='itemscope' itemtype='http://schema.org/BlogPosting'> <meta content='https://static.righto.com/images/555a/555-w300.jpg' itemprop='image_url'/> <meta content='6264947694886887540' itemprop='blogId'/> <meta content='7887791316595824502' itemprop='postId'/> <a name='7887791316595824502'></a> <h3 class='post-title entry-title' itemprop='name'> <a href='http://www.righto.com/2022/01/silicon-die-teardown-look-inside-early.html'>Silicon die teardown: a look inside an early 555 timer chip</a> </h3> <div class='post-header'> <div class='post-header-line-1'></div> </div> <div class='post-body entry-content' id='post-body-7887791316595824502' itemprop='description articleBody'> <style> .hilite {cursor:zoom-in} a:link img.hilite, a:visited img.hilite { color: #fff;} </style> <p>If you've played around with electronic circuits, you probably know the 555 timer integrated circuit,<span id="fnref:POPULAR"><a class="ref" href="#fn:POPULAR">1</a></span> said to be the world's best-selling integrated circuit with billions sold. Designed by analog IC wizard Hans Camenzind<span id="fnref:CAMENZIND"><a class="ref" href="#fn:CAMENZIND">2</a></span>, the 555 has been called one of the <a href="http://spectrum.ieee.org/semiconductors/processors/25-microchips-that-shook-the-world">greatest chips of all time</a>.</p> <p><a href="https://static.righto.com/images/555a/555.jpg"><img alt="An 8-pin 555 timer with a Signetics logo. It doesn't have a 555 label, but instead is labeled "52B 01003" with a 7304 date code, indicating week 4 of 1973. Photo courtesy of Eric Schlaepfer." class="hilite" height="302" src="https://static.righto.com/images/555a/555-w300.jpg" title="An 8-pin 555 timer with a Signetics logo. It doesn't have a 555 label, but instead is labeled "52B 01003" with a 7304 date code, indicating week 4 of 1973. Photo courtesy of Eric Schlaepfer." width="300" /></a><div class="cite">An 8-pin 555 timer with a Signetics logo. It doesn't have a 555 label, but instead is labeled "52B 01003" with a 7304 date code, indicating week 4 of 1973. Photo courtesy of Eric Schlaepfer.</div></p> <p>Eric Schlaepfer (<a href="https://twitter.com/TubeTimeUS/status/1481120280105811970">@TubeTimeUS</a>) recently came across the chip above, with a mysterious part number. He tediously sanded through the epoxy package to reveal the die (below) and determined that the chip is a 555 timer. Signetics released the 555 timer in mid-1972 <span id="fnref:1972"><a class="ref" href="#fn:1972">4</a></span> and the chip below has a January 1973 date code (7304), so it must be one of the first 555 timers. Curiously, it is not labeled 555, so perhaps it is a prototype or internal version.<span id="fnref:revisions"><a class="ref" href="#fn:revisions">3</a></span> I took detailed die photos, which I discuss in this blog post.</p> <p><a href="https://static.righto.com/images/555a/package.jpg"><img alt="The 555 timer with the package sanded down to expose the silicon die, the tiny square in the middle." class="hilite" height="270" src="https://static.righto.com/images/555a/package-w500.jpg" title="The 555 timer with the package sanded down to expose the silicon die, the tiny square in the middle." width="500" /></a><div class="cite">The 555 timer with the package sanded down to expose the silicon die, the tiny square in the middle.</div></p> <h2>A brief explanation of the 555 timer</h2> <p>The 555 timer has hundreds of applications, operating as anything from a timer or latch to a voltage-controlled oscillator or modulator. The diagram below illustrates how the 555 timer operates as a simple oscillator. Inside the 555 chip, three resistors form a divider generating references voltages of 1/3 and 2/3 of the supply voltage. The external capacitor will charge and discharge between these limits, producing an oscillation. In more detail, the capacitor will slowly charge (A) through the external resistors until its voltage hits the 2/3 reference. At that point (B), the upper (threshold) comparator switches the flip flop off and the output off. This turns on the discharge transistor, slowly discharging the capacitor (C). When the voltage on the capacitor hits the 1/3 reference (D), the lower (trigger) comparator turns on, setting the flip flop and the output, and the cycle repeats. The values of the resistors and capacitor control the timing, from microseconds to hours.<span id="fnref:BRILLIANT"><a class="ref" href="#fn:BRILLIANT">5</a></span></p> <p><a href="https://static.righto.com/images/555a/555-operation.png"><img alt="Diagram showing how the 555 timer can operate as an oscillator. The external capacitor charges and discharges through the external resistors, under the control of the 555 timer." class="hilite" height="349" src="https://static.righto.com/images/555a/555-operation-w800.png" title="Diagram showing how the 555 timer can operate as an oscillator. The external capacitor charges and discharges through the external resistors, under the control of the 555 timer." width="800" /></a><div class="cite">Diagram showing how the 555 timer can operate as an oscillator. The external capacitor charges and discharges through the external resistors, under the control of the 555 timer.</div></p> <p>To summarize, the key components of the 555 timer are the comparators to detect the upper and lower voltage limits, the three-resistor divider to set these limits, and the flip flop to keep track of whether the circuit is charging or discharging. The 555 timer has two other pins (reset and control voltage) that I haven't covered above; they can be used for more complex circuits.</p> <h2>The structure of the integrated circuit</h2> <p>I created the photo below from a composite of microscope images. On top of the silicon, a thin layer of metal connects different parts of the chip. This metal is clearly visible in the photo as light-colored traces. Under the metal, a thin, glassy silicon dioxide layer provides insulation between the metal and the silicon, except where contact holes in the silicon dioxide allow the metal to connect to the silicon. At the edge of the chip, thin wires connect the metal pads to the chip's external pins.</p> <p><a href="https://static.righto.com/images/555a/die.jpg"><img alt="Die photo of the 555 timer. Click this image (or any other) for a larger version." class="hilite" height="652" src="https://static.righto.com/images/555a/die-w700.jpg" title="Die photo of the 555 timer. Click this image (or any other) for a larger version." width="700" /></a><div class="cite">Die photo of the 555 timer. Click this image (or any other) for a larger version.</div></p> <p>The different types of silicon on the chip are harder to see. Regions of the chip are treated (<a href="https://en.wikipedia.org/wiki/Doping_(semiconductor)">doped</a>) with impurities to change the electrical properties of the silicon. N-type silicon has an excess of electrons (negative), while P-type silicon lacks electrons (positive). In the photo, these regions show up as a slightly different color surrounded by a thin black border. These regions are the building blocks of the chip, forming transistors and resistors.</p> <h3>NPN transistors inside the IC</h3> <p>Transistors are the key components in a chip. The 555 timer uses NPN and PNP bipolar transistors. If you've studied electronics, you've probably seen a diagram of an NPN transistor like the one below, showing the collector (C), base (B), and emitter (E) of the transistor, The transistor is illustrated as a sandwich of P silicon in between two symmetric layers of N silicon; the N-P-N layers make an NPN transistor. It turns out that transistors on a chip look nothing like this, and the base often isn't even in the middle!</p> <p><a href="https://static.righto.com/images/555a/npn-transistor.png"><img alt="Schematic symbol for an NPN transistor, along with an oversimplified diagram of its internal structure." class="hilite" height="167" src="https://static.righto.com/images/555a/npn-transistor-w250.png" title="Schematic symbol for an NPN transistor, along with an oversimplified diagram of its internal structure." width="250" /></a><div class="cite">Schematic symbol for an NPN transistor, along with an oversimplified diagram of its internal structure.</div></p> <p>The photo below shows a closeup of one of the transistors in the 555 as it appears on the chip. The slightly different tints in the silicon indicate regions that have been doped to form N and P regions. The whitish areas are the metal layer of the chip on top of the silicon - these form the wires connecting to the collector, emitter, and base.</p> <p><a href="https://static.righto.com/images/555a/transistor-structure-npn.jpg"><img alt="Structure of an NPN transistor on the die." class="hilite" height="300" src="https://static.righto.com/images/555a/transistor-structure-npn-w350.jpg" title="Structure of an NPN transistor on the die." width="350" /></a><div class="cite">Structure of an NPN transistor on the die.</div></p> <p>Underneath the photo is a cross-section drawing illustrating how the transistor is constructed. There's a lot more than just the N-P-N sandwich you see in books, but if you look carefully at the vertical cross-section below the 'E', you can find the N-P-N that forms the transistor. The emitter (E) wire is connected to N+ silicon. Below that is a P layer connected to the base contact (B). And below that is an N+ layer connected (indirectly) to the collector (C).<span id="fnref:EMITTER"><a class="ref" href="#fn:EMITTER">6</a></span> The transistor is surrounded by a P+ ring that isolates it from neighboring components.</p> <h3>PNP transistors inside the IC</h3> <p>You might expect PNP transistors to be similar to NPN transistors, just swapping the roles of N and P silicon. But for a variety of reasons, PNP transistors have an entirely different construction. They consist of a small circular emitter (P), surrounded by a ring-shaped base (N), which is surrounded by the collector (P). This forms a P-N-P sandwich horizontally (laterally), unlike the vertical structure of the NPN transistors. <P> The diagram below shows one of the PNP transistors in the 555, along with a cross-section showing the silicon structure. Note that although the metal contact for the base is on the edge of the transistor, it is electrically connected through the N and N+ regions to its active ring in between the collector and emitter.</p> <p><a href="https://static.righto.com/images/555a/transistor-structure-pnp.jpg"><img alt="A PNP transistor in the 555 timer chip. Connections for the collector (C), emitter (E) and base (B) are labeled, along with N and P doped silicon. The base forms a ring around the emitter, and the collector forms a ring around the base." class="hilite" height="369" src="https://static.righto.com/images/555a/transistor-structure-pnp-w400.jpg" title="A PNP transistor in the 555 timer chip. Connections for the collector (C), emitter (E) and base (B) are labeled, along with N and P doped silicon. The base forms a ring around the emitter, and the collector forms a ring around the base." width="400" /></a><div class="cite">A PNP transistor in the 555 timer chip. Connections for the collector (C), emitter (E) and base (B) are labeled, along with N and P doped silicon. The base forms a ring around the emitter, and the collector forms a ring around the base.</div></p> <p>The output transistors in the 555 are much larger than the other transistors and have a different structure in order to produce the high-current output. The photo below shows one of the output transistors. Note the multiple interlocking "fingers" of the emitter and base, surrounded by the large collector.</p> <p><a href="https://static.righto.com/images/555a/big-transistor.jpg"><img alt="A large, high-current NPN output transistor in the 555 timer chip. The collector (C), base (B) and emitter (E) are labeled." class="hilite" height="283" src="https://static.righto.com/images/555a/big-transistor-w400.jpg" title="A large, high-current NPN output transistor in the 555 timer chip. The collector (C), base (B) and emitter (E) are labeled." width="400" /></a><div class="cite">A large, high-current NPN output transistor in the 555 timer chip. The collector (C), base (B) and emitter (E) are labeled.</div></p> <h3>How resistors are implemented in silicon</h3> <p>Resistors are a key component of analog chips. Unfortunately, resistors in ICs are large and inaccurate; the resistances can vary by 50% from chip to chip. Thus, analog ICs are designed so only the ratio of resistors matters, not the absolute values, since the ratios remain nearly constant.</p> <p><a href="https://static.righto.com/images/555a/resistor.jpg"><img alt="A resistor inside the 555 timer. The resistor is a strip of P silicon between two metal contacts." class="hilite" height="130" src="https://static.righto.com/images/555a/resistor-w500.jpg" title="A resistor inside the 555 timer. The resistor is a strip of P silicon between two metal contacts." width="500" /></a><div class="cite">A resistor inside the 555 timer. The resistor is a strip of P silicon between two metal contacts.</div></p> <p>The photo above shows a 10K&ohm; resistor in the 555, formed from a strip of P silicon (pinkish gray), contacting metal wiring at either end. Other metal wires cross the resistor. The resistor has a spiral shape to fit its length in the available space. The resistor below is a 100K&ohm; <i>pinch resistor</i>. A layer of N silicon on top of the pinch resistor makes the conductive region much thinner (i.e. pinches it), forming a much higher but less accurate resistance.</p> <p><a href="https://static.righto.com/images/555a/pinch-resistor.jpg"><img alt="A pinch resistor inside the 555 timer. The resistor is a strip of P silicon between two metal contacts. An N layer on top pinches the resistor and increases the resistance. This resistor is crossed by a vertical metal line." class="hilite" height="107" src="https://static.righto.com/images/555a/pinch-resistor-w300.jpg" title="A pinch resistor inside the 555 timer. The resistor is a strip of P silicon between two metal contacts. An N layer on top pinches the resistor and increases the resistance. This resistor is crossed by a vertical metal line." width="300" /></a><div class="cite">A pinch resistor inside the 555 timer. The resistor is a strip of P silicon between two metal contacts. An N layer on top pinches the resistor and increases the resistance. This resistor is crossed by a vertical metal line.</div></p> <h3>IC component: The current mirror</h3> <p>There are some subcircuits that are very common in analog ICs, but may seem mysterious at first. The current mirror is one of these. If you've looked at analog IC block diagrams, you may have seen the symbols below, indicating a current source, and wondered what a current source is and why you'd use one. The idea is you start with one known current and then you can "clone" multiple copies of the current with a simple transistor circuit, the current mirror.</p> <p><a href="https://static.righto.com/images/555a/current-source.png"><img alt="Schematic symbols for a current source." class="hilite" height="131" src="https://static.righto.com/images/555a/current-source-w200.png" title="Schematic symbols for a current source." width="200" /></a><div class="cite">Schematic symbols for a current source.</div></p> <p>The following circuit shows how a current mirror is implemented with two identical transistors.<span id="fnref:CURRENTMIRROR"><a class="ref" href="#fn:CURRENTMIRROR">7</a></span> A reference current passes through the transistor on the right. (In this case, the current is set by the resistor.) Since both transistors have the same emitter voltage and base voltage, they source the same current, so the current on the right matches the reference current on the left.<span id="fnref:q19"><a class="ref" href="#fn:q19">8</a></span></p> <p><a href="https://static.righto.com/images/555a/current-mirror.png"><img alt="Current mirror circuit. The current on the right copies the current on the left." class="hilite" height="262" src="https://static.righto.com/images/555a/current-mirror-w250.png" title="Current mirror circuit. The current on the right copies the current on the left." width="250" /></a><div class="cite">Current mirror circuit. The current on the right copies the current on the left.</div></p> <p>A common use of a current mirror is to replace resistors. As explained earlier, resistors inside ICs are both inconveniently large and inaccurate. It saves space to use a current mirror instead of a resistor whenever possible. Also, the currents produced by a current mirror are nearly identical, unlike the currents produced by two resistors.</p> <p><a href="https://static.righto.com/images/555a/trans-mirror-labeled.jpg"><img alt="Three transistors form a current mirror in the 555 timer chip. They all share the same base and two transistors share emitters." class="hilite" height="231" src="https://static.righto.com/images/555a/trans-mirror-labeled-w500.jpg" title="Three transistors form a current mirror in the 555 timer chip. They all share the same base and two transistors share emitters." width="500" /></a><div class="cite">Three transistors form a current mirror in the 555 timer chip. They all share the same base and two transistors share emitters.</div></p> <p>The three transistors above form a current mirror with two outputs. Note the three transistors share the base connection, tied to the collector on the right, and the emitters on the right are tied together. On the schematic, the two transistors on the right are drawn as a single two-collector transistor, Q19.</p> <h3>IC component: The differential pair</h3> <p>The second important circuit to understand is the differential pair, the most common two-transistor subcircuit used in analog ICs. <span id="fnref:DIFFERENTIALPAIR"><a class="ref" href="#fn:DIFFERENTIALPAIR">9</a></span> You may have wondered how a comparator compares two voltages, or an op amp subtracts two voltages. This is the job of the differential pair.</p> <p><a href="https://static.righto.com/images/555a/differential-pair.png"><img alt="Schematic of a simple differential pair circuit. The current source sends a fixed current I through the differential pair. If the two inputs are equal, the current is split equally." class="hilite" height="299" src="https://static.righto.com/images/555a/differential-pair-w250.png" title="Schematic of a simple differential pair circuit. The current source sends a fixed current I through the differential pair. If the two inputs are equal, the current is split equally." width="250" /></a><div class="cite">Schematic of a simple differential pair circuit. The current source sends a fixed current I through the differential pair. If the two inputs are equal, the current is split equally.</div></p> <p>The schematic above shows a simple differential pair. The current source at the bottom provides a fixed current I, which is split between the two input transistors. If the input voltages are equal, the current will be split equally into the two branches (I1 and I2). If one of the input voltages is a bit higher than the other, the corresponding transistor will conduct exponentially more current, so one branch gets more current and the other branch gets less. A small input difference is enough to direct most of the current into the "winning" branch, flipping the comparator on or off. The 555 chip uses one differential pair for the threshold comparator and another for the trigger comparator.<span id="fnref:comparators"><a class="ref" href="#fn:comparators">10</a></span></p> <h2>The 555 schematic interactive explorer</h2> <p>The 555 die photo and schematic<span id="fnref:schematic"><a class="ref" href="#fn:schematic">11</a></span> below are interactive. Click on a component in the die or schematic, and a brief explanation of the component will be displayed. (For a thorough discussion of how the 555 timer works, see <a href="http://shop.emscdn.com/KitInstrux/555/555_principles_revB3.pdf">555 Principles of Operation</a>.)</p> <p>For a quick overview, the large output transistors and discharge transistor are the most obvious features on the die. The threshold comparator consists of Q1 through Q8. The trigger comparator consists of Q10 through Q13, along with current mirror Q9. Q16 and Q17 form the flip flop. The three 5K&ohm; resistors forming the voltage divider are in the middle of the chip.<span id="fnref:parallel"><a class="ref" href="#fn:parallel">12</a></span> Urban legend says that the 555 is named after these three 5K resistors, but <a href="http://www.semiconductormuseum.com/Transistors/LectureHall/Camenzind/Camenzind_Page2.htm">according to its designer</a> 555 is just an arbitrary number in the 500 chip series.</p> <div id="die555canvasholder" class="chipcanvasholder" style="width:750px;height:693px"> <canvas id="die555can2"></canvas> <canvas id="die555can1"></canvas> </div> <div id="chiptext555" class="chiptext" style="width: 736px;">Click the die or schematic for details...</div> <div id="schematic555canvasholder" class="chipcanvasholder" style="width:750px;height:538px"> <canvas id="schematic555can2"></canvas> <canvas id="schematic555can1"></canvas> </div> <style type="text/css"> .chiptext { border: 2px solid gray; margin-bottom:7px; min-height: 2.5em; padding: 5px; font-family:sans-serif; width: 536px; } .chipcanvasholder { display: inline-block; height: 600px; position: relative; width: 800px; } .chipcanvasholder canvas { position: absolute; top: 0; left: 0; } </style> <script src="https://ajax.googleapis.com/ajax/libs/jquery/1/jquery.min.js"></script> <script src="https://static.righto.com/555a/die-555.js"></script> <script src="https://static.righto.com/555a/schematic-555.js"></script> <script src="https://static.righto.com/555a/notes-555.js"></script> <script src="https://static.righto.com/555a/chip-viewer-555.js"></script>  <script type="text/javascript"> $(document).ready(function() { var controller = { hilite: function(id) { if (notes[id]) { $('#chiptext555').html(notes[id]); } else { $('#chiptext555').html(''); } view1.unhilite(); view1.ctx2.strokeStyle = 'rgba(0,0,0,0)'; if (view1.data[id].type == 'NPN') { view1.ctx2.fillStyle = 'rgba(0,0,255,0.2)'; } else if (view1.data[id].type == 'PNP') { view1.ctx2.fillStyle = 'rgba(255,0,0,0.2)'; } else { view1.ctx2.fillStyle = 'rgba(0,255,0,0.2)'; } view2.ctx2.fillStyle = view1.ctx2.fillStyle; view1.drawDataBox(id, view1.ctx2); view1.ctx2.fillStyle = 'rgba(255,0,255,0.8)'; view1.drawDataFeature(id, view1.ctx2, false); view1.hilite(); view2.unhilite(); view2.ctx2.strokeStyle = 'rgba(0,0,0,0)'; view2.drawDataBox(id, view2.ctx2); view2.hilite(); }, unhilite: function(id) { $('#chiptext').html(''); view1.unhilite(id); view2.unhilite(id); }, loaded: function(view) { view.ctx1.font = 'bold 18px arial'; view.ctx1.fillStyle = 'rgba(0,0,100,1)'; view1.pinColor = 'white'; view1.componentColor = '#0cc'; view.ctx2.font = 'bold 16px arial'; if (view == view1) { view1.drawDataFeatures(view1.ctx1, true); } }, }; var view1 = new View(die555Data, "die555", "https://static.righto.com/images/555a/die-small.jpg", controller, 750); var view2 = new View(schematic555Data, "schematic555", "https://static.righto.com/images/555a/schematic-philips.png", controller, 800, 541); }); </script> <h2>Conclusion</h2> <p>I hope you've found this look inside the 555 timer chip interesting. Next time you're building a <a href="http://makezine.com/2012/08/24/555-timer-weekend-projects/">555 project</a>, you'll know exactly what's inside the chip. I've written about the <a href="https://www.righto.com/2016/02/555-timer-teardown-inside-worlds-most.html">555 timer before</a>; this post is pretty much the same as that one but with a different die. I've also written about <a href="https://www.righto.com/2016/04/teardown-of-cmos-555-timer-chip-how.html">a CMOS version</a>. Thanks to Eric Schlaepfer<span id="fnref:EMS"><a class="ref" href="#fn:EMS">13</a></span> for providing the die; see <a href="https://twitter.com/TubeTimeUS/status/1481120280105811970">his Twitter thread</a> for background on this chip.</p> <p>I announce my latest blog posts on Twitter, so follow me <a href="https://twitter.com/kenshirriff">@kenshirriff</a> and you won't miss an article! I also have an <a href="http://www.righto.com/feeds/posts/default">RSS feed</a>.</p> <h2>Notes and references</h2> <div class="footnote"> <ol> <li id="fn:POPULAR"> <p>The 555 timer is iconic enough to appear on <a href="https://www.spreadshirt.com/555+timer+mugs+&+drinkware">mugs</a>, <a href="https://www.spreadshirt.com/555+timer+bags+&+backpacks">bags</a>, <a href="http://www.zazzle.co.uk/555+timer+gifts">caps</a> and <a href="https://teespring.com/555timer-grey3">t-shirts</a>. Whole books are devoted to <a target="_blank" href="https://www.amazon.com/s/ref=as_li_ss_tl?_encoding=UTF8&camp=1789&creative=390957&fst=as%3Aoff&keywords=555%20timer&linkCode=ur2&qid=1448837596&rh=n%3A283155%2Ck%3A555%20timer&sort=relevancerank&tag=rightocom&linkId=TXV2AQJUMMXQUHBP">555</a> <a href="https://archive.org/details/electronics_-_Forrest_Mims-engineers_mini-notebook_555_timer_circuits_radio_sha">timer</a> <a href="http://chiclassiccomp.org/docs/content/books/ICTimerCookbook1stEd1977_WalterGJung.pdf">circuits</a>. <a class="footnote-backref" href="#fnref:POPULAR" title="Jump back to footnote 1 in the text">↩</a></p> </li> <li id="fn:CAMENZIND"> <p>The book <i>Designing Analog Chips</i> written by the 555's inventor Hans Camenzind is really interesting, and I recommend it if you want to know how analog chips work. Chapter 11 has an extensive discussion of the 555's history and operation. Page 11-3 claims the 555 has been the best-selling IC every year, although I don't know if that is still true. The free PDF is <a href="http://www.designinganalogchips.com/">here</a> or get <a rel="nofollow" href="https://www.amazon.com/gp/product/1589397185/ref=as_li_tl?ie=UTF8&camp=1789&creative=390957&creativeASIN=1589397185&linkCode=as2&tag=rightocom&linkId=GEY5H6J5JINDRNMP">the book</a>. <a class="footnote-backref" href="#fnref:CAMENZIND" title="Jump back to footnote 2 in the text">↩</a></p> </li> <li id="fn:revisions"> <p>The die has the part number 1000 and revision "C", so this probably corresponds to the 01003 number on the package. I suspect this chip is the third mask revision of the original 555.</p> <p><a href="https://static.righto.com/images/555a/die-wikipedia.jpg"><img alt="The first 555 die with the part number "1000" highlighted and the revision "A" magnified." class="hilite" height="329" src="https://static.righto.com/images/555a/die-wikipedia-w300.jpg" title="The first 555 die with the part number "1000" highlighted and the revision "A" magnified." width="300" /></a><div class="cite">The first 555 die with the part number "1000" highlighted and the revision "A" magnified.</div></p> <p>The die of the first 555 timer version (above) is marked with the number "1000" and revision "A". I compared this image with the die photo that I took and I couldn't see any differences except the revision changed to "C". The mask changes must have been fairly subtle. (This image is at <a href="https://en.wikipedia.org/wiki/555_timer_IC#/media/File:Die_of_the_first_555_chip.jpg">Wikipedia</a> and <a href="https://spectrum.ieee.org/25-microchips-that-shook-the-world">IEEE Spectrum</a>. The image is captioned as the die shot of the first 555 timer IC manufactured in 1971.) <a class="footnote-backref" href="#fnref:revisions" title="Jump back to footnote 3 in the text">↩</a></p> </li> <li id="fn:1972"> <p>The 555 chip was introduced in mid-1972 according to <a href="http://www.bitsavers.org/components/signetics/_dataBooks/1979_Signetics_Analog_Applications.pdf">Signetics Analog Applications</a> page 149. <a class="footnote-backref" href="#fnref:1972" title="Jump back to footnote 4 in the text">↩</a></p> </li> <li id="fn:BRILLIANT"> <p>The brilliant part of the 555 timer is that the oscillation frequency depends only on the external resistors and capacitor and is insensitive to the supply voltage. If the supply voltage drops, the 1/3 and 2/3 references drop too, so you might expect the oscillations to be faster. But the lower voltage charges the capacitor more slowly, canceling this out and keeping the frequency constant.</p> <p>This voltage insensitivity is so tricky that the chip's designer didn't figure it out until near the end of the 555's design, but it made a big difference. The original design was more complex and required nine pins, which is a terrible size for an IC since there are no packages between 8 and 14 pins. The final, simpler 555 design worked with 8 pins, making the chip's packaging much cheaper. (See page 11-3 of <i>Designing Analog Chips</i> for the full story.) <a class="footnote-backref" href="#fnref:BRILLIANT" title="Jump back to footnote 5 in the text">↩</a></p> </li> <li id="fn:EMITTER"> <p>You might have wondered why there is a distinction between the collector and emitter of a transistor, when the typical diagram of a transistor is symmetrical. As you can see from the die photo, the collector and emitter are very different in a real transistor. In addition to the very large size difference, the silicon doping is different. The result is a transistor will have <a href="https://en.wikibooks.org/wiki/Semiconductors/Introduce_to_Transistor#Operating_Modes">poor gain</a> if the collector and emitter are swapped. <a class="footnote-backref" href="#fnref:EMITTER" title="Jump back to footnote 6 in the text">↩</a></p> </li> <li id="fn:CURRENTMIRROR"> <p>For more information about current mirrors, check <a href="https://en.wikipedia.org/wiki/Current_mirror">wikipedia</a>, any analog IC book, or chapter 3 of <a href="http://www.designinganalogchips.com/_count/designinganalogchips.pdf">Designing Analog Chips</a>. <a class="footnote-backref" href="#fnref:CURRENTMIRROR" title="Jump back to footnote 7 in the text">↩</a></p> </li> <li id="fn:q19"> <p>The schematic has the unusual symbol below, which indicates a transistor with two collectors. The base is drawn on the same side as the emitter and collectors, which adds to the confusion. On the die, this transistor is implemented with two separate transistors, with the emitters and the bases wired together. Other circuits sometimes use a single transistor that has two physical collectors present.</p> <p><a href="https://static.righto.com/images/555a/q19.png"><img alt="This symbol indicates a transistor with two collectors." class="hilite" height="131" src="https://static.righto.com/images/555a/q19-w100.png" title="This symbol indicates a transistor with two collectors." width="100" /></a><div class="cite">This symbol indicates a transistor with two collectors.</div></p> <p> <a class="footnote-backref" href="#fnref:q19" title="Jump back to footnote 8 in the text">↩</a></p> </li> <li id="fn:DIFFERENTIALPAIR"> <p>Differential pairs are also called long-tailed pairs. According to <a href="https://www.amazon.com/gp/product/0470245999/ref=as_li_tl?ie=UTF8&camp=1789&creative=390957&creativeASIN=0470245999&linkCode=as2&tag=rightocom&linkId=M7Y4IGG5INYYFPEW">Analysis and Design of Analog Integrated Circuits</a> the differential pair is "perhaps the most widely used two-transistor subcircuits in monolithic analog circuits." (p214) For more information about differential pairs, see <a href="https://en.wikipedia.org/wiki/Differential_amplifier#Long-tailed_pair">wikipedia</a>, any analog IC book, or chapter 4 of <em>Designing Analog Chips</em>. <a class="footnote-backref" href="#fnref:DIFFERENTIALPAIR" title="Jump back to footnote 9 in the text">↩</a></p> </li> <li id="fn:comparators"> <p>In the 555, the threshold comparator uses NPN transistors, while the trigger comparator uses PNP transistors. This allows the threshold comparator to work near the supply voltage and the trigger comparator to work near ground. The 555's comparators also use two transistors on each input (<a href="https://en.wikipedia.org/wiki/Darlington_transistor">Darlington pair</a>) to buffer the inputs. <a class="footnote-backref" href="#fnref:comparators" title="Jump back to footnote 10 in the text">↩</a></p> </li> <li id="fn:schematic"> <p>The 555 schematic used in this article is from the <a href="http://pdf.datasheetcatalog.com/datasheet/philips/NE_SA_SE555_C_2.pdf">Philips datasheet</a>. It is identical to the <a href="http://www.bitsavers.org/components/signetics/_dataBooks/1979_Signetics_Analog_Applications.pdf">Signetics schematic</a> p150. <a class="footnote-backref" href="#fnref:schematic" title="Jump back to footnote 11 in the text">↩</a></p> </li> <li id="fn:parallel"> <p>Note that the three resistors for the voltage divider are parallel and next to each other. This helps ensure they have the same resistance even if there are electrical variations across the silicon. <a class="footnote-backref" href="#fnref:parallel" title="Jump back to footnote 12 in the text">↩</a></p> </li> <li id="fn:EMS"> <p>Evil Mad Scientist sells a very cool <a href="http://shop.evilmadscientist.com/productsmenu/tinykitlist/652"> discrete 555 timer kit</a>, duplicating the 555 circuit on a larger scale with individual transistors and resistors — it actually works as a 555 replacement. Their <a href="http://www.evilmadscientist.com/2011/555-footstool/">555 footstool</a> is also worth a look.</p> <p><a href="https://static.righto.com/images/555a/evilmadscientist.png"><img alt="Large-size 555 timer created by Evil Mad Scientist Lab." class="hilite" height="375" src="https://static.righto.com/images/555a/evilmadscientist-w500.png" title="Large-size 555 timer created by Evil Mad Scientist Lab." width="500" /></a><div class="cite">Large-size 555 timer created by Evil Mad Scientist Lab.</div></p> <p> <a class="footnote-backref" href="#fnref:EMS" title="Jump back to footnote 13 in the text">↩</a></p> </li> </ol> </div> <div style='clear: both;'></div> </div> <div class='post-footer'> <div class='post-footer-line post-footer-line-1'><span class='post-comment-link'> <a class='comment-link' href='https://www.blogger.com/comment/fullpage/post/6264947694886887540/7887791316595824502' onclick=''> 7 comments: </a> </span> <span class='post-icons'> <span class='item-action'> <a href='https://www.blogger.com/email-post/6264947694886887540/7887791316595824502' title='Email Post'> <img alt='' class='icon-action' height='13' src='http://img1.blogblog.com/img/icon18_email.gif' width='18'/> </a> </span> <span class='item-control blog-admin pid-1138732533'> <a href='https://www.blogger.com/post-edit.g?blogID=6264947694886887540&postID=7887791316595824502&from=pencil' title='Edit Post'> <img alt='' class='icon-action' height='18' src='https://resources.blogblog.com/img/icon18_edit_allbkg.gif' width='18'/> </a> </span> </span> <span class='post-backlinks post-comment-link'> </span> <div class='post-share-buttons goog-inline-block'> <a class='goog-inline-block share-button sb-email' href='https://www.blogger.com/share-post.g?blogID=6264947694886887540&postID=7887791316595824502&target=email' target='_blank' title='Email This'><span class='share-button-link-text'>Email This</span></a><a class='goog-inline-block share-button sb-blog' href='https://www.blogger.com/share-post.g?blogID=6264947694886887540&postID=7887791316595824502&target=blog' onclick='window.open(this.href, "_blank", "height=270,width=475"); return false;' target='_blank' title='BlogThis!'><span class='share-button-link-text'>BlogThis!</span></a><a class='goog-inline-block share-button sb-twitter' href='https://www.blogger.com/share-post.g?blogID=6264947694886887540&postID=7887791316595824502&target=twitter' target='_blank' title='Share to X'><span class='share-button-link-text'>Share to X</span></a><a class='goog-inline-block share-button sb-facebook' href='https://www.blogger.com/share-post.g?blogID=6264947694886887540&postID=7887791316595824502&target=facebook' onclick='window.open(this.href, "_blank", "height=430,width=640"); return false;' target='_blank' title='Share to Facebook'><span class='share-button-link-text'>Share to Facebook</span></a><a class='goog-inline-block share-button sb-pinterest' href='https://www.blogger.com/share-post.g?blogID=6264947694886887540&postID=7887791316595824502&target=pinterest' target='_blank' title='Share to Pinterest'><span class='share-button-link-text'>Share to Pinterest</span></a> </div> </div> <div class='post-footer-line post-footer-line-2'><span class='post-labels'> Labels: <a href='http://www.righto.com/search/label/chips' rel='tag'>chips</a>, <a href='http://www.righto.com/search/label/electronics' rel='tag'>electronics</a>, <a href='http://www.righto.com/search/label/reverse-engineering' rel='tag'>reverse-engineering</a> </span> </div> <div class='post-footer-line post-footer-line-3'></div> </div> </div> </div> </div></div> </div> <div class='blog-pager' id='blog-pager'> <span id='blog-pager-newer-link'> <a class='blog-pager-newer-link' href='http://www.righto.com/search?updated-max=2022-04-09T11:22:00-07:00&max-results=7&reverse-paginate=true' id='Blog1_blog-pager-newer-link' title='Newer Posts'>Newer Posts</a> </span> <span id='blog-pager-older-link'> <a class='blog-pager-older-link' href='http://www.righto.com/search?updated-max=2022-01-24T09:10:00-08:00&max-results=7' id='Blog1_blog-pager-older-link' title='Older Posts'>Older Posts</a> </span> <a class='home-link' href='http://www.righto.com/'>Home</a> </div> <div class='clear'></div> </div></div> </div> </div> <div class='column-left-outer'> <div class='column-left-inner'> <aside> </aside> </div> </div> <div class='column-right-outer'> <div class='column-right-inner'> <aside> <div class='sidebar section' id='sidebar-right-1'><div class='widget HTML' data-version='1' id='HTML2'> <div class='widget-content'> <style> @import url('https://fonts.googleapis.com/css?family=Montserrat:300,400,500,700'); .form-preview { display: flex; flex-direction: column; justify-content: center; margin-top: 30px; padding: clamp(17px, 5%, 40px) clamp(17px, 7%, 50px); max-width: 350px; min-height: 200px; border-radius: 6px; box-shadow: 0 5px 25px rgba(34, 60, 47, 0.25); } .form-preview, .form-preview *{ box-sizing: border-box; } .form-preview .preview-heading { width: 100%; } .form-preview .preview-heading h5{ margin-top: 0; margin-bottom: 0; } .form-preview .preview-input-field { margin-top: 20px; width: 100%; } .form-preview .preview-input-field input { width: 100%; height: 40px; border-radius: 6px; border: 2px solid #e9e8e8; background-color: #fff; outline: none; } .form-preview .preview-input-field input::placeholder, .form-preview .preview-input-field input { opacity: 0.5; color: #000; font-family: "Montserrat"; font-size: 14px; font-weight: 500; line-height: 20px; text-align: center; } .form-preview .preview-submit-button { margin-top: 10px; width: 100%; } .form-preview .preview-submit-button button { width: 100%; height: 40px; border: 0; border-radius: 6px; line-height: 0px; } .form-preview .preview-submit-button button:hover { cursor: pointer; } </style><form data-v-4c58e686="" action="https://api.follow.it/subscription-form/U3NBTmZKVkI1YVpCa000a0RCZHFiQ3FYMko1cWRTZTN6K3hJdWM2QWxJbE1uVXdXUHZZVzJVQzVLZGh5Y0RCVXB2d2JSTzBobGhuY0FsZnlHbVdFZ2VTN2Q4Vy84RnIxUTgzVlcrbXNIR0Y0aW93d3REM2J6VS9RL0gxWURnV1d8ZWN0YStwUWdWWUFiOTIyWDVGWjdYYVdGZEVNcC9qODZacjlwWXRIcEJQRT0=/8" method="post"><div data-v-4c58e686="" class="form-preview" style="background-color: rgb(255, 255, 255); border-style: solid; border-width: 1px; border-color: rgb(204, 204, 204); position: relative;"><div data-v-4c58e686="" class="preview-heading"><h5 data-v-4c58e686="" style="font-family: Montserrat; font-weight: bold; color: rgb(0, 0, 0); font-size: 12px; text-align: center;">Get new posts by email:</h5></div> <div data-v-4c58e686="" class="preview-input-field"><input data-v-4c58e686="" type="email" name="email" placeholder="Enter your email" spellcheck="false" /></div> <div data-v-4c58e686="" class="preview-submit-button"><button data-v-4c58e686="" type="submit" style="font-family: Montserrat; font-weight: bold; color: rgb(255, 255, 255); font-size: 12px; text-align: center; background-color: rgb(0, 0, 0);">Subscribe</button></div></div></form> </div> <div class='clear'></div> </div><div class='widget HTML' data-version='1' id='HTML3'> <h2 class='title'>About the site</h2> <div class='widget-content'> <a href="https://www.righto.com/p/index.html">Contact info and site index</a> </div> <div class='clear'></div> </div><div class='widget PopularPosts' data-version='1' id='PopularPosts1'> <h2>Popular Posts</h2> <div class='widget-content popular-posts'> <ul> <li> <div class='item-thumbnail-only'> <div class='item-thumbnail'> <a href='http://www.righto.com/2025/03/mother-of-all-demos-usb-keyset-interface.html' target='_blank'> <img alt='' border='0' src='https://lh3.googleusercontent.com/blogger_img_proxy/AEn0k_sUBR6-eoH7AycDSCgF7L5-48Z7gd3VA0gI-ddEoCp1zcIYOR2PzuOOVNqXXlRMK_8NWZ_IGueTV_b-4j1W_kBTDv8rxR7At8wtLEWVXeYSskHK8B0nmfzdeJ9e1d-izdE=w72-h72-p-k-no-nu'/> </a> </div> <div class='item-title'><a href='http://www.righto.com/2025/03/mother-of-all-demos-usb-keyset-interface.html'>A USB interface to the "Mother of All Demos" keyset</a></div> </div> <div style='clear: both;'></div> </li> <li> <div class='item-thumbnail-only'> <div class='item-thumbnail'> <a href='http://www.righto.com/2025/03/pentium-microcde-rom-circuitry.html' target='_blank'> <img alt='' border='0' src='https://lh3.googleusercontent.com/blogger_img_proxy/AEn0k_tNvcrlW0n1ClWN4QRyZHQ91WDbl9CBnY1Bj8JAAkSxtrmMnhUQUy0mewCdY2APQZ2Bd3sGy4NUN7Zi_Sq93Rv6ZnglQ7fmxIeC0LloInt4OpJlUlxYjJ1Du-ityzcyXcIF_FHrUQAKQD1bR9_qTCg=w72-h72-p-k-no-nu'/> </a> </div> <div class='item-title'><a href='http://www.righto.com/2025/03/pentium-microcde-rom-circuitry.html'>Notes on the Pentium's microcode circuitry</a></div> </div> <div style='clear: both;'></div> </li> <li> <div class='item-thumbnail-only'> <div class='item-thumbnail'> <a href='http://www.righto.com/2024/05/blog-post.html' target='_blank'> <img alt='' border='0' src='https://lh3.googleusercontent.com/blogger_img_proxy/AEn0k_udKqJ3dawEpB4rnUfAQJupdi05dtzM2IGK_pvqN81NQ4a-viU-MFyh73YLeaoW8R-b7ORGJPW0aulpmsY07poaVB5uySCYJlYbI0Wx167-o116xdzCvolrZ1dhjdjyqS8XGKSESrEzVYzwIqeqAnHF=w72-h72-p-k-no-nu'/> </a> </div> <div class='item-title'><a href='http://www.righto.com/2024/05/blog-post.html'>Inside a vintage aerospace navigation computer of uncertain purpose</a></div> </div> <div style='clear: both;'></div> </li> <li> <div class='item-thumbnail-only'> <div class='item-thumbnail'> <a href='http://www.righto.com/2025/03/pentium-multiplier-adder-reverse-engineered.html' target='_blank'> <img alt='' border='0' src='https://lh3.googleusercontent.com/blogger_img_proxy/AEn0k_tBNI17JqSkMQ7yAZoXcapS42rn1GvAkBUspgvE0yKgYYObPs3CEiRmPRdIpBM5zBFowqCiuM1QVhyCsAEnHPoRRQiO_u9OjK0-QWgkyCo9Y-3UAZbR899o9ae2JmH4si8fIgJyAdSVgf0v=w72-h72-p-k-no-nu'/> </a> </div> <div class='item-title'><a href='http://www.righto.com/2025/03/pentium-multiplier-adder-reverse-engineered.html'>The Pentium contains a complicated circuit to multiply by three</a></div> </div> <div style='clear: both;'></div> </li> <li> <div class='item-thumbnail-only'> <div class='item-thumbnail'> <a href='http://www.righto.com/2009/08/multi-protocol-infrared-remote-library.html' target='_blank'> <img alt='' border='0' src='https://lh3.googleusercontent.com/blogger_img_proxy/AEn0k_sMJPqeEtGjgaUEppCbnH1hqJ-fNyUrxcyp16ffLjT-hBm4iYv7cUDT1XkJFqnOmZ508mcOaKBJL0O1bFrhExY3ELt17jp3VP7Jl75z5yVl-zU=w72-h72-p-k-no-nu'/> </a> </div> <div class='item-title'><a href='http://www.righto.com/2009/08/multi-protocol-infrared-remote-library.html'>A Multi-Protocol Infrared Remote Library for the Arduino</a></div> </div> <div style='clear: both;'></div> </li> <li> <div class='item-thumbnail-only'> <div class='item-thumbnail'> <a href='http://www.righto.com/2012/10/a-dozen-usb-chargers-in-lab-apple-is.html' target='_blank'> <img alt='' border='0' src='https://lh3.googleusercontent.com/blogger_img_proxy/AEn0k_uR1CJEeo3W0VOfKkBPg8qhCm5kOLRvaZSBULMgBfwT7g1zeXLhnPKK9421517mXN5J1pGwSdxkT-Ot1Btp4F6L_iSTmEQuEzy_O4UsLsdxXUKb3p8CRlhx2xK03Q0=w72-h72-p-k-no-nu'/> </a> </div> <div class='item-title'><a href='http://www.righto.com/2012/10/a-dozen-usb-chargers-in-lab-apple-is.html'>A dozen USB chargers in the lab: Apple is very good, but not quite the best</a></div> </div> <div style='clear: both;'></div> </li> <li> <div class='item-thumbnail-only'> <div class='item-thumbnail'> <a href='http://www.righto.com/2012/05/apple-iphone-charger-teardown-quality.html' target='_blank'> <img alt='' border='0' src='https://lh3.googleusercontent.com/blogger_img_proxy/AEn0k_uGL8l345fobDFFiNChKE2ptcligU8ZdF0yEBrSwV_PGEAwVrgHtJDTEQDzmjSN41Nja45QE4KrOMEBRsUxTQ22VAC8hdAEepD-wTDDKHqGrFFGsXVtapRVDEuZ6EyxScMyURkxqc3YzlnAB8KVtnZyCe4=w72-h72-p-k-no-nu'/> </a> </div> <div class='item-title'><a href='http://www.righto.com/2012/05/apple-iphone-charger-teardown-quality.html'>Apple iPhone charger teardown: quality in a tiny expensive package</a></div> </div> <div style='clear: both;'></div> </li> <li> <div class='item-thumbnail-only'> <div class='item-thumbnail'> <a href='http://www.righto.com/2014/09/mining-bitcoin-with-pencil-and-paper.html' target='_blank'> <img alt='' border='0' src='https://lh3.googleusercontent.com/blogger_img_proxy/AEn0k_uW-8_mSIhQy51T1-Fm1a1wVxhqtslmgwZt5KyCVzA6j9sYI1d846F4sz_znqFuMs_qEiL5pd2t51Vmd-A3vIU6q58TWzh2bX_320yQJYlNROgSUgX1-easIrPGgjaSdfbC=w72-h72-p-k-no-nu'/> </a> </div> <div class='item-title'><a href='http://www.righto.com/2014/09/mining-bitcoin-with-pencil-and-paper.html'>Mining Bitcoin with pencil and paper: 0.67 hashes per day</a></div> </div> <div style='clear: both;'></div> </li> </ul> <div class='clear'></div> </div> </div><div class='widget BlogSearch' data-version='1' id='BlogSearch1'> <h2 class='title'>Search This Blog</h2> <div class='widget-content'> <div id='BlogSearch1_form'> <form action='http://www.righto.com/search' class='gsc-search-box' target='_top'> <table cellpadding='0' cellspacing='0' class='gsc-search-box'> <tbody> <tr> <td class='gsc-input'> <input autocomplete='off' class='gsc-input' name='q' size='10' title='search' type='text' value=''/> </td> <td class='gsc-search-button'> <input class='gsc-search-button' title='search' type='submit' value='Search'/> </td> </tr> </tbody> </table> </form> </div> </div> <div class='clear'></div> </div><div class='widget Label' data-version='1' id='Label1'> <h2>Labels</h2> <div class='widget-content cloud-label-widget-content'> <span class='label-size label-size-2'> <a dir='ltr' href='http://www.righto.com/search/label/386'>386</a> </span> <span class='label-size label-size-3'> <a dir='ltr' href='http://www.righto.com/search/label/6502'>6502</a> </span> <span class='label-size label-size-2'> <a dir='ltr' href='http://www.righto.com/search/label/8008'>8008</a> </span> <span class='label-size label-size-3'> <a dir='ltr' href='http://www.righto.com/search/label/8085'>8085</a> </span> <span class='label-size label-size-4'> <a dir='ltr' href='http://www.righto.com/search/label/8086'>8086</a> </span> <span class='label-size label-size-2'> <a dir='ltr' href='http://www.righto.com/search/label/8087'>8087</a> </span> <span class='label-size label-size-2'> <a dir='ltr' href='http://www.righto.com/search/label/8088'>8088</a> </span> <span class='label-size label-size-3'> <a dir='ltr' href='http://www.righto.com/search/label/aerospace'>aerospace</a> </span> <span class='label-size label-size-3'> <a dir='ltr' href='http://www.righto.com/search/label/alto'>alto</a> </span> <span class='label-size label-size-3'> <a dir='ltr' href='http://www.righto.com/search/label/analog'>analog</a> </span> <span class='label-size label-size-3'> <a dir='ltr' href='http://www.righto.com/search/label/Apollo'>Apollo</a> </span> <span class='label-size label-size-3'> <a dir='ltr' href='http://www.righto.com/search/label/apple'>apple</a> </span> <span class='label-size label-size-4'> <a dir='ltr' href='http://www.righto.com/search/label/arc'>arc</a> </span> <span class='label-size label-size-3'> <a dir='ltr' href='http://www.righto.com/search/label/arduino'>arduino</a> </span> <span class='label-size label-size-3'> <a dir='ltr' href='http://www.righto.com/search/label/arm'>arm</a> </span> <span class='label-size label-size-2'> <a dir='ltr' href='http://www.righto.com/search/label/beaglebone'>beaglebone</a> </span> <span class='label-size label-size-3'> <a dir='ltr' href='http://www.righto.com/search/label/bitcoin'>bitcoin</a> </span> <span class='label-size label-size-1'> <a dir='ltr' href='http://www.righto.com/search/label/c%23'>c#</a> </span> <span class='label-size label-size-2'> <a dir='ltr' href='http://www.righto.com/search/label/cadc'>cadc</a> </span> <span class='label-size label-size-2'> <a dir='ltr' href='http://www.righto.com/search/label/calculator'>calculator</a> </span> <span class='label-size label-size-4'> <a dir='ltr' href='http://www.righto.com/search/label/chips'>chips</a> </span> <span class='label-size label-size-2'> <a dir='ltr' href='http://www.righto.com/search/label/css'>css</a> </span> <span class='label-size label-size-1'> <a dir='ltr' href='http://www.righto.com/search/label/datapoint'>datapoint</a> </span> <span class='label-size label-size-2'> <a dir='ltr' href='http://www.righto.com/search/label/dx7'>dx7</a> </span> <span class='label-size label-size-5'> <a dir='ltr' href='http://www.righto.com/search/label/electronics'>electronics</a> </span> <span class='label-size label-size-1'> <a dir='ltr' href='http://www.righto.com/search/label/f%23'>f#</a> </span> <span class='label-size label-size-1'> <a dir='ltr' href='http://www.righto.com/search/label/fairchild'>fairchild</a> </span> <span class='label-size label-size-2'> <a dir='ltr' href='http://www.righto.com/search/label/fpga'>fpga</a> </span> <span class='label-size label-size-2'> <a dir='ltr' href='http://www.righto.com/search/label/fractals'>fractals</a> </span> <span class='label-size label-size-2'> <a dir='ltr' href='http://www.righto.com/search/label/genome'>genome</a> </span> <span class='label-size label-size-2'> <a dir='ltr' href='http://www.righto.com/search/label/globus'>globus</a> </span> <span class='label-size label-size-1'> <a dir='ltr' href='http://www.righto.com/search/label/haskell'>haskell</a> </span> <span class='label-size label-size-1'> <a dir='ltr' href='http://www.righto.com/search/label/HP'>HP</a> </span> <span class='label-size label-size-2'> <a dir='ltr' href='http://www.righto.com/search/label/html5'>html5</a> </span> <span class='label-size label-size-3'> <a dir='ltr' href='http://www.righto.com/search/label/ibm'>ibm</a> </span> <span class='label-size label-size-3'> <a dir='ltr' href='http://www.righto.com/search/label/ibm1401'>ibm1401</a> </span> <span class='label-size label-size-2'> <a dir='ltr' href='http://www.righto.com/search/label/ibm360'>ibm360</a> </span> <span class='label-size label-size-4'> <a dir='ltr' href='http://www.righto.com/search/label/intel'>intel</a> </span> <span class='label-size label-size-2'> <a dir='ltr' href='http://www.righto.com/search/label/ipv6'>ipv6</a> </span> <span class='label-size label-size-3'> <a dir='ltr' href='http://www.righto.com/search/label/ir'>ir</a> </span> <span class='label-size label-size-2'> <a dir='ltr' href='http://www.righto.com/search/label/java'>java</a> </span> <span class='label-size label-size-2'> <a dir='ltr' href='http://www.righto.com/search/label/javascript'>javascript</a> </span> <span class='label-size label-size-3'> <a dir='ltr' href='http://www.righto.com/search/label/math'>math</a> </span> <span class='label-size label-size-3'> <a dir='ltr' href='http://www.righto.com/search/label/microcode'>microcode</a> </span> <span class='label-size label-size-2'> <a dir='ltr' href='http://www.righto.com/search/label/oscilloscope'>oscilloscope</a> </span> <span class='label-size label-size-3'> <a dir='ltr' href='http://www.righto.com/search/label/Pentium'>Pentium</a> </span> <span class='label-size label-size-2'> <a dir='ltr' href='http://www.righto.com/search/label/photo'>photo</a> </span> <span class='label-size label-size-4'> <a dir='ltr' href='http://www.righto.com/search/label/power%20supply'>power supply</a> </span> <span class='label-size label-size-4'> <a dir='ltr' href='http://www.righto.com/search/label/random'>random</a> </span> <span class='label-size label-size-5'> <a dir='ltr' href='http://www.righto.com/search/label/reverse-engineering'>reverse-engineering</a> </span> <span class='label-size label-size-2'> <a dir='ltr' href='http://www.righto.com/search/label/sheevaplug'>sheevaplug</a> </span> <span class='label-size label-size-3'> <a dir='ltr' href='http://www.righto.com/search/label/snark'>snark</a> </span> <span class='label-size label-size-3'> <a dir='ltr' href='http://www.righto.com/search/label/space'>space</a> </span> <span class='label-size label-size-2'> <a dir='ltr' href='http://www.righto.com/search/label/spanish'>spanish</a> </span> <span class='label-size label-size-2'> <a dir='ltr' href='http://www.righto.com/search/label/synth'>synth</a> </span> <span class='label-size label-size-4'> <a dir='ltr' href='http://www.righto.com/search/label/teardown'>teardown</a> </span> <span class='label-size label-size-2'> <a dir='ltr' href='http://www.righto.com/search/label/theory'>theory</a> </span> <span class='label-size label-size-1'> <a dir='ltr' href='http://www.righto.com/search/label/unicode'>unicode</a> </span> <span class='label-size label-size-2'> <a dir='ltr' href='http://www.righto.com/search/label/Z-80'>Z-80</a> </span> <div class='clear'></div> </div> </div><div class='widget BlogArchive' data-version='1' id='BlogArchive1'> <h2>Blog Archive</h2> <div class='widget-content'> <div id='ArchiveList'> <div id='BlogArchive1_ArchiveList'> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2025/'> 2025 </a> <span class='post-count' dir='ltr'>(8)</span> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2025/03/'> March </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2025/02/'> February </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2025/01/'> January </a> <span class='post-count' dir='ltr'>(4)</span> </li> </ul> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2024/'> 2024 </a> <span class='post-count' dir='ltr'>(21)</span> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2024/12/'> December </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2024/11/'> November </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2024/10/'> October </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2024/09/'> September </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2024/08/'> August </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2024/07/'> July </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2024/06/'> June </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2024/05/'> May </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2024/04/'> April </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2024/03/'> March </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2024/02/'> February </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2024/01/'> January </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2023/'> 2023 </a> <span class='post-count' dir='ltr'>(35)</span> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2023/12/'> December </a> <span class='post-count' dir='ltr'>(4)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2023/11/'> November </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2023/10/'> October </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2023/09/'> September </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2023/08/'> August </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2023/07/'> July </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2023/05/'> May </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2023/04/'> April </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2023/03/'> March </a> <span class='post-count' dir='ltr'>(4)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2023/02/'> February </a> <span class='post-count' dir='ltr'>(5)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2023/01/'> January </a> <span class='post-count' dir='ltr'>(8)</span> </li> </ul> </li> </ul> <ul class='hierarchy'> <li class='archivedate expanded'> <a class='toggle' href='javascript:void(0)'> <span class='zippy toggle-open'> ▼  </span> </a> <a class='post-count-link' href='http://www.righto.com/2022/'> 2022 </a> <span class='post-count' dir='ltr'>(18)</span> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2022/11/'> November </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2022/08/'> August </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2022/07/'> July </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2022/06/'> June </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2022/05/'> May </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2022/04/'> April </a> <span class='post-count' dir='ltr'>(4)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2022/03/'> March </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2022/02/'> February </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate expanded'> <a class='toggle' href='javascript:void(0)'> <span class='zippy toggle-open'> ▼  </span> </a> <a class='post-count-link' href='http://www.righto.com/2022/01/'> January </a> <span class='post-count' dir='ltr'>(2)</span> <ul class='posts'> <li><a href='http://www.righto.com/2022/01/ibm360model50.html'>Simulating the IBM 360/50 mainframe from its micro...</a></li> <li><a href='http://www.righto.com/2022/01/silicon-die-teardown-look-inside-early.html'>Silicon die teardown: a look inside an early 555 t...</a></li> </ul> </li> </ul> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2021/'> 2021 </a> <span class='post-count' dir='ltr'>(26)</span> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2021/12/'> December </a> <span class='post-count' dir='ltr'>(4)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2021/11/'> November </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2021/09/'> September </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2021/08/'> August </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2021/07/'> July </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2021/06/'> June </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2021/05/'> May </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2021/04/'> April </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2021/03/'> March </a> <span class='post-count' dir='ltr'>(4)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2021/02/'> February </a> <span class='post-count' dir='ltr'>(4)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2021/01/'> January </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2020/'> 2020 </a> <span class='post-count' dir='ltr'>(33)</span> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2020/12/'> December </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2020/11/'> November </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2020/10/'> October </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2020/09/'> September </a> <span class='post-count' dir='ltr'>(4)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2020/08/'> August </a> <span class='post-count' dir='ltr'>(5)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2020/07/'> July </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2020/06/'> June </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2020/05/'> May </a> <span class='post-count' dir='ltr'>(4)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2020/04/'> April </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2020/03/'> March </a> <span class='post-count' dir='ltr'>(5)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2020/01/'> January </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2019/'> 2019 </a> <span class='post-count' dir='ltr'>(18)</span> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2019/11/'> November </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2019/10/'> October </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2019/09/'> September </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2019/08/'> August </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2019/07/'> July </a> <span class='post-count' dir='ltr'>(4)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2019/04/'> April </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2019/02/'> February </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2019/01/'> January </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2018/'> 2018 </a> <span class='post-count' dir='ltr'>(17)</span> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2018/12/'> December </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2018/09/'> September </a> <span class='post-count' dir='ltr'>(4)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2018/08/'> August </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2018/06/'> June </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2018/05/'> May </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2018/04/'> April </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2018/03/'> March </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2018/02/'> February </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2018/01/'> January </a> <span class='post-count' dir='ltr'>(4)</span> </li> </ul> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2017/'> 2017 </a> <span class='post-count' dir='ltr'>(21)</span> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2017/12/'> December </a> <span class='post-count' dir='ltr'>(5)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2017/11/'> November </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2017/10/'> October </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2017/08/'> August </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2017/07/'> July </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2017/06/'> June </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2017/04/'> April </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2017/03/'> March </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2017/02/'> February </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2017/01/'> January </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2016/'> 2016 </a> <span class='post-count' dir='ltr'>(34)</span> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2016/12/'> December </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2016/10/'> October </a> <span class='post-count' dir='ltr'>(5)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2016/09/'> September </a> <span class='post-count' dir='ltr'>(8)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2016/08/'> August </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2016/07/'> July </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2016/06/'> June </a> <span class='post-count' dir='ltr'>(4)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2016/05/'> May </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2016/04/'> April </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2016/03/'> March </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2016/02/'> February </a> <span class='post-count' dir='ltr'>(4)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2016/01/'> January </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2015/'> 2015 </a> <span class='post-count' dir='ltr'>(12)</span> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2015/12/'> December </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2015/11/'> November </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2015/10/'> October </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2015/08/'> August </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2015/05/'> May </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2015/03/'> March </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2015/02/'> February </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2014/'> 2014 </a> <span class='post-count' dir='ltr'>(13)</span> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2014/12/'> December </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2014/10/'> October </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2014/09/'> September </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2014/05/'> May </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2014/03/'> March </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2014/02/'> February </a> <span class='post-count' dir='ltr'>(5)</span> </li> </ul> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2013/'> 2013 </a> <span class='post-count' dir='ltr'>(24)</span> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2013/11/'> November </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2013/09/'> September </a> <span class='post-count' dir='ltr'>(4)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2013/08/'> August </a> <span class='post-count' dir='ltr'>(4)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2013/07/'> July </a> <span class='post-count' dir='ltr'>(4)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2013/06/'> June </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2013/04/'> April </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2013/03/'> March </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2013/02/'> February </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2013/01/'> January </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2012/'> 2012 </a> <span class='post-count' dir='ltr'>(10)</span> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2012/12/'> December </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2012/11/'> November </a> <span class='post-count' dir='ltr'>(5)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2012/10/'> October </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2012/05/'> May </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2012/03/'> March </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2012/02/'> February </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2011/'> 2011 </a> <span class='post-count' dir='ltr'>(11)</span> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2011/12/'> December </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2011/07/'> July </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2011/05/'> May </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2011/04/'> April </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2011/03/'> March </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2011/02/'> February </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2010/'> 2010 </a> <span class='post-count' dir='ltr'>(22)</span> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2010/12/'> December </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2010/11/'> November </a> <span class='post-count' dir='ltr'>(4)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2010/10/'> October </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2010/08/'> August </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2010/06/'> June </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2010/05/'> May </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2010/04/'> April </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2010/03/'> March </a> <span class='post-count' dir='ltr'>(4)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2010/01/'> January </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2009/'> 2009 </a> <span class='post-count' dir='ltr'>(22)</span> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2009/12/'> December </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2009/11/'> November </a> <span class='post-count' dir='ltr'>(5)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2009/09/'> September </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2009/08/'> August </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2009/07/'> July </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2009/06/'> June </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2009/04/'> April </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2009/03/'> March </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2009/02/'> February </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2009/01/'> January </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2008/'> 2008 </a> <span class='post-count' dir='ltr'>(27)</span> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2008/07/'> July </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2008/06/'> June </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2008/05/'> May </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2008/04/'> April </a> <span class='post-count' dir='ltr'>(4)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2008/03/'> March </a> <span class='post-count' dir='ltr'>(10)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2008/02/'> February </a> <span class='post-count' dir='ltr'>(6)</span> </li> </ul> </li> </ul> </div> </div> <div class='clear'></div> </div> </div></div> </aside> </div> </div> </div> <div style='clear: both'></div>  </div>  </div> </div> <div class='main-cap-bottom cap-bottom'> <div class='cap-left'></div> <div class='cap-right'></div> </div> </div> <footer> <div class='footer-outer'> <div class='footer-cap-top cap-top'> <div class='cap-left'></div> <div class='cap-right'></div> </div> <div class='fauxborder-left footer-fauxborder-left'> <div class='fauxborder-right footer-fauxborder-right'></div> <div class='region-inner footer-inner'> <div class='foot no-items section' id='footer-1'></div> <table border='0' cellpadding='0' cellspacing='0' class='section-columns columns-2'> <tbody> <tr> <td class='first columns-cell'> <div class='foot no-items section' id='footer-2-1'></div> </td> <td class='columns-cell'> <div class='foot no-items section' id='footer-2-2'></div> </td> </tr> </tbody> </table>  <div class='foot section' id='footer-3'><div class='widget Attribution' data-version='1' id='Attribution1'> <div class='widget-content' style='text-align: center;'> Powered by <a href='https://www.blogger.com' target='_blank'>Blogger</a>. </div> <div class='clear'></div> </div></div> </div> </div> <div class='footer-cap-bottom cap-bottom'> <div class='cap-left'></div> <div class='cap-right'></div> </div> </div> </footer>  </div> </div> <div class='content-cap-bottom cap-bottom'> <div class='cap-left'></div> <div class='cap-right'></div> </div> </div> </div> <script type='text/javascript'> window.setTimeout(function() { document.body.className = document.body.className.replace('loading', ''); }, 10); </script> <script type="text/javascript" src="https://www.blogger.com/static/v1/widgets/2806328968-widgets.js"></script> <script type='text/javascript'> window['__wavt'] = 'AOuZoY7i5D9KT4BPEaGp-DCmf7Bx9k1Frg:1743990588296';_WidgetManager._Init('//www.blogger.com/rearrange?blogID\x3d6264947694886887540','//www.righto.com/2022/01/','6264947694886887540'); _WidgetManager._SetDataContext([{'name': 'blog', 'data': {'blogId': '6264947694886887540', 'title': 'Ken Shirriff\x27s blog', 'url': 'http://www.righto.com/2022/01/', 'canonicalUrl': 'http://www.righto.com/2022/01/', 'homepageUrl': 'http://www.righto.com/', 'searchUrl': 'http://www.righto.com/search', 'canonicalHomepageUrl': 'http://www.righto.com/', 'blogspotFaviconUrl': 'http://www.righto.com/favicon.ico', 'bloggerUrl': 'https://www.blogger.com', 'hasCustomDomain': true, 'httpsEnabled': false, 'enabledCommentProfileImages': true, 'gPlusViewType': 'FILTERED_POSTMOD', 'adultContent': false, 'analyticsAccountNumber': 'UA-3782444-1', 'encoding': 'UTF-8', 'locale': 'en', 'localeUnderscoreDelimited': 'en', 'languageDirection': 'ltr', 'isPrivate': false, 'isMobile': false, 'isMobileRequest': false, 'mobileClass': '', 'isPrivateBlog': false, 'isDynamicViewsAvailable': true, 'feedLinks': '\x3clink rel\x3d\x22alternate\x22 type\x3d\x22application/atom+xml\x22 title\x3d\x22Ken Shirriff\x26#39;s blog - Atom\x22 href\x3d\x22http://www.righto.com/feeds/posts/default\x22 /\x3e\n\x3clink rel\x3d\x22alternate\x22 type\x3d\x22application/rss+xml\x22 title\x3d\x22Ken Shirriff\x26#39;s blog - RSS\x22 href\x3d\x22http://www.righto.com/feeds/posts/default?alt\x3drss\x22 /\x3e\n\x3clink rel\x3d\x22service.post\x22 type\x3d\x22application/atom+xml\x22 title\x3d\x22Ken Shirriff\x26#39;s blog - Atom\x22 href\x3d\x22https://www.blogger.com/feeds/6264947694886887540/posts/default\x22 /\x3e\n', 'meTag': '', 'adsenseHostId': 'ca-host-pub-1556223355139109', 'adsenseHasAds': false, 'adsenseAutoAds': false, 'boqCommentIframeForm': true, 'loginRedirectParam': '', 'view': '', 'dynamicViewsCommentsSrc': '//www.blogblog.com/dynamicviews/4224c15c4e7c9321/js/comments.js', 'dynamicViewsScriptSrc': '//www.blogblog.com/dynamicviews/2c423cb85ff27b65', 'plusOneApiSrc': 'https://apis.google.com/js/platform.js', 'disableGComments': true, 'interstitialAccepted': false, 'sharing': {'platforms': [{'name': 'Get link', 'key': 'link', 'shareMessage': 'Get link', 'target': ''}, {'name': 'Facebook', 'key': 'facebook', 'shareMessage': 'Share to Facebook', 'target': 'facebook'}, {'name': 'BlogThis!', 'key': 'blogThis', 'shareMessage': 'BlogThis!', 'target': 'blog'}, {'name': 'X', 'key': 'twitter', 'shareMessage': 'Share to X', 'target': 'twitter'}, {'name': 'Pinterest', 'key': 'pinterest', 'shareMessage': 'Share to Pinterest', 'target': 'pinterest'}, {'name': 'Email', 'key': 'email', 'shareMessage': 'Email', 'target': 'email'}], 'disableGooglePlus': true, 'googlePlusShareButtonWidth': 0, 'googlePlusBootstrap': '\x3cscript type\x3d\x22text/javascript\x22\x3ewindow.___gcfg \x3d {\x27lang\x27: \x27en\x27};\x3c/script\x3e'}, 'hasCustomJumpLinkMessage': false, 'jumpLinkMessage': 'Read more', 'pageType': 'archive', 'pageName': 'January 2022', 'pageTitle': 'Ken Shirriff\x27s blog: January 2022'}}, {'name': 'features', 'data': {}}, {'name': 'messages', 'data': {'edit': 'Edit', 'linkCopiedToClipboard': 'Link copied to clipboard!', 'ok': 'Ok', 'postLink': 'Post Link'}}, {'name': 'template', 'data': {'name': 'custom', 'localizedName': 'Custom', 'isResponsive': false, 'isAlternateRendering': false, 'isCustom': true}}, {'name': 'view', 'data': {'classic': {'name': 'classic', 'url': '?view\x3dclassic'}, 'flipcard': {'name': 'flipcard', 'url': '?view\x3dflipcard'}, 'magazine': {'name': 'magazine', 'url': '?view\x3dmagazine'}, 'mosaic': {'name': 'mosaic', 'url': '?view\x3dmosaic'}, 'sidebar': {'name': 'sidebar', 'url': '?view\x3dsidebar'}, 'snapshot': {'name': 'snapshot', 'url': '?view\x3dsnapshot'}, 'timeslide': {'name': 'timeslide', 'url': '?view\x3dtimeslide'}, 'isMobile': false, 'title': 'Ken Shirriff\x27s blog', 'description': 'Computer history, restoring vintage computers, IC reverse engineering, and whatever', 'url': 'http://www.righto.com/2022/01/', 'type': 'feed', 'isSingleItem': false, 'isMultipleItems': true, 'isError': false, 'isPage': false, 'isPost': false, 'isHomepage': false, 'isArchive': true, 'isLabelSearch': false, 'archive': {'year': 2022, 'month': 1, 'rangeMessage': 'Showing posts from January, 2022'}}}]); _WidgetManager._RegisterWidget('_HeaderView', new _WidgetInfo('Header1', 'header', document.getElementById('Header1'), {}, 'displayModeFull')); _WidgetManager._RegisterWidget('_BlogView', new _WidgetInfo('Blog1', 'main', document.getElementById('Blog1'), {'cmtInteractionsEnabled': false}, 'displayModeFull')); _WidgetManager._RegisterWidget('_HTMLView', new _WidgetInfo('HTML2', 'sidebar-right-1', document.getElementById('HTML2'), {}, 'displayModeFull')); _WidgetManager._RegisterWidget('_HTMLView', new _WidgetInfo('HTML3', 'sidebar-right-1', document.getElementById('HTML3'), {}, 'displayModeFull')); _WidgetManager._RegisterWidget('_PopularPostsView', new _WidgetInfo('PopularPosts1', 'sidebar-right-1', document.getElementById('PopularPosts1'), {}, 'displayModeFull')); _WidgetManager._RegisterWidget('_BlogSearchView', new _WidgetInfo('BlogSearch1', 'sidebar-right-1', document.getElementById('BlogSearch1'), {}, 'displayModeFull')); _WidgetManager._RegisterWidget('_LabelView', new _WidgetInfo('Label1', 'sidebar-right-1', document.getElementById('Label1'), {}, 'displayModeFull')); _WidgetManager._RegisterWidget('_BlogArchiveView', new _WidgetInfo('BlogArchive1', 'sidebar-right-1', document.getElementById('BlogArchive1'), {'languageDirection': 'ltr', 'loadingMessage': 'Loading\x26hellip;'}, 'displayModeFull')); _WidgetManager._RegisterWidget('_AttributionView', new _WidgetInfo('Attribution1', 'footer-3', document.getElementById('Attribution1'), {}, 'displayModeFull')); </script> </body> </html>