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<div class="vector-body-before-content"> <div class="mw-indicators"> </div> <div id="siteSub" class="noprint">From Wikipedia, the free encyclopedia</div> </div> <div id="contentSub"><div id="mw-content-subtitle"></div></div> <div id="mw-content-text" class="mw-body-content"><div class="mw-content-ltr mw-parser-output" lang="en" dir="ltr"><div class="shortdescription nomobile noexcerpt noprint searchaux" style="display:none">Operating system</div> <div class="shortdescription nomobile noexcerpt noprint searchaux" style="display:none">Operating system</div> <style data-mw-deduplicate="TemplateStyles:r1257001546">.mw-parser-output .infobox-subbox{padding:0;border:none;margin:-3px;width:auto;min-width:100%;font-size:100%;clear:none;float:none;background-color:transparent}.mw-parser-output .infobox-3cols-child{margin:auto}.mw-parser-output .infobox .navbar{font-size:100%}@media screen{html.skin-theme-clientpref-night .mw-parser-output .infobox-full-data:not(.notheme)>div:not(.notheme)[style]{background:#1f1f23!important;color:#f8f9fa}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .infobox-full-data:not(.notheme) div:not(.notheme){background:#1f1f23!important;color:#f8f9fa}}@media(min-width:640px){body.skin--responsive .mw-parser-output .infobox-table{display:table!important}body.skin--responsive .mw-parser-output .infobox-table>caption{display:table-caption!important}body.skin--responsive .mw-parser-output .infobox-table>tbody{display:table-row-group}body.skin--responsive .mw-parser-output .infobox-table tr{display:table-row!important}body.skin--responsive .mw-parser-output .infobox-table th,body.skin--responsive .mw-parser-output .infobox-table td{padding-left:inherit;padding-right:inherit}}</style><table class="infobox vevent"><caption class="infobox-title summary">Incompatible Timesharing System (ITS)</caption><tbody><tr><th scope="row" class="infobox-label" style="white-space: nowrap;"><a href="/wiki/Programmer" title="Programmer">Developer</a></th><td class="infobox-data"><a href="/wiki/MIT_Artificial_Intelligence_Laboratory" class="mw-redirect" title="MIT Artificial Intelligence Laboratory">MIT Artificial Intelligence Laboratory</a> and <a href="/wiki/Project_MAC" class="mw-redirect" title="Project MAC">Project MAC</a></td></tr><tr><th scope="row" class="infobox-label" style="white-space: nowrap;"><a href="/wiki/Programming_language" title="Programming language">Written in</a></th><td class="infobox-data"><a href="/wiki/Assembly_language" title="Assembly language">Assembly language</a></td></tr><tr><th scope="row" class="infobox-label" style="white-space: nowrap;">Working state</th><td class="infobox-data">Active</td></tr><tr><th scope="row" class="infobox-label" style="white-space: nowrap;">Initial release</th><td class="infobox-data">July 1967<span class="noprint">; 57 years ago</span><span style="display:none"> (<span class="bday dtstart published updated">1967-07</span>)</span><sup id="cite_ref-1" class="reference"><a href="#cite_note-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup></td></tr><tr><th scope="row" class="infobox-label" style="white-space: nowrap;"><a href="/wiki/Repository_(version_control)" title="Repository (version control)">Repository</a></th><td class="infobox-data"><span class="url"><a rel="nofollow" class="external text" href="https://github.com/PDP-10/its">github<wbr />.com<wbr />/PDP-10<wbr />/its</a></span></td></tr><tr><th scope="row" class="infobox-label" style="white-space: nowrap;"><a href="/wiki/Natural_language" title="Natural language">Available in</a></th><td class="infobox-data"><a href="/wiki/English_language" title="English language">English</a></td></tr><tr><th scope="row" class="infobox-label" style="white-space: nowrap;">Platforms</th><td class="infobox-data">Digital <a href="/wiki/PDP-6" title="PDP-6">PDP-6</a>, <a href="/wiki/PDP-10" title="PDP-10">PDP-10</a>, (<a href="/wiki/Emulator" title="Emulator">emulators</a> now available)</td></tr><tr><th scope="row" class="infobox-label" style="white-space: nowrap;"><a href="/wiki/User_interface" title="User interface">Default<br />user interface</a></th><td class="infobox-data"><a href="/wiki/Command-line_interface" title="Command-line interface">Command-line interface</a> (<a href="/wiki/Dynamic_debugging_technique" title="Dynamic debugging technique">DDT</a>)</td></tr><tr><th scope="row" class="infobox-label" style="white-space: nowrap;"><a href="/wiki/Software_license" title="Software license">License</a></th><td class="infobox-data"><a href="/wiki/GPL-3.0-or-later" class="mw-redirect" title="GPL-3.0-or-later">GPL-3.0-or-later</a><sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup></td></tr></tbody></table> <p><b>Incompatible Timesharing System</b> (<b>ITS</b>) is a <a href="/wiki/Time-sharing" title="Time-sharing">time-sharing</a> <a href="/wiki/Operating_system" title="Operating system">operating system</a> developed principally by the <a href="/wiki/MIT_Artificial_Intelligence_Laboratory" class="mw-redirect" title="MIT Artificial Intelligence Laboratory">MIT Artificial Intelligence Laboratory</a>, with help from <a href="/wiki/Project_MAC" class="mw-redirect" title="Project MAC">Project MAC</a>. The name is the jocular complement of the MIT <a href="/wiki/Compatible_Time-Sharing_System" title="Compatible Time-Sharing System">Compatible Time-Sharing System</a> (CTSS). </p><p>ITS, and the software developed on it, were technically and culturally influential far beyond their core user community. Remote "guest" or "tourist" access was easily available via the early <a href="/wiki/ARPANET" title="ARPANET">ARPANET</a>, allowing many interested parties to informally try out features of the operating system and application programs. The wide-open ITS philosophy and collaborative online community were a major influence on the <a href="/wiki/Hacker_culture" title="Hacker culture">hacker culture</a>, as described in Steven Levy's book <i><a href="/wiki/Hackers:_Heroes_of_the_Computer_Revolution" title="Hackers: Heroes of the Computer Revolution">Hackers</a></i>,<sup id="cite_ref-LevyWL_3-0" class="reference"><a href="#cite_note-LevyWL-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> and were the direct forerunners of the <a href="/wiki/Free_and_open-source_software" title="Free and open-source software">free and open-source software</a> (FOSS), <a href="/wiki/Open-design_movement" title="Open-design movement">open-design</a>, and <a href="/wiki/Wiki" title="Wiki">Wiki</a> movements. </p> <meta property="mw:PageProp/toc" /> <div class="mw-heading mw-heading2"><h2 id="History">History</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Incompatible_Timesharing_System&action=edit&section=1" title="Edit section: History"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>ITS development was initiated in the late 1960s by those (the majority of the MIT AI Lab staff at that time) who disagreed with the direction taken by Project MAC's <a href="/wiki/Multics" title="Multics">Multics</a> project (which had started in the mid-1960s), particularly such decisions as the inclusion of powerful <a href="/wiki/Computer_security" title="Computer security">system security</a>. The name was chosen by <a href="/wiki/Tom_Knight_(scientist)" title="Tom Knight (scientist)">Tom Knight</a> as a joke on the name of the earliest MIT time-sharing operating system, the <a href="/wiki/Compatible_Time-Sharing_System" title="Compatible Time-Sharing System">Compatible Time-Sharing System</a> (CTSS), which dated from the early 1960s.<sup id="cite_ref-LevyWL_3-1" class="reference"><a href="#cite_note-LevyWL-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> </p><p>By simplifying their system compared to Multics, ITS's authors<sup class="noprint Inline-Template" style="white-space:nowrap;">[<i><a href="/wiki/Wikipedia:Manual_of_Style/Words_to_watch#Unsupported_attributions" title="Wikipedia:Manual of Style/Words to watch"><span title="The material near this tag possibly uses too-vague attribution or weasel words. (February 2025)">who?</span></a></i>]</sup> were able to quickly<sup class="noprint Inline-Template" style="margin-left:0.1em; white-space:nowrap;">[<i><a href="/wiki/Wikipedia:Please_clarify" title="Wikipedia:Please clarify"><span title="vague (May 2016)">clarification needed</span></a></i>]</sup> produce a functional operating system for their lab.<sup id="cite_ref-stuart_4-0" class="reference"><a href="#cite_note-stuart-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup> ITS was written in <a href="/wiki/Assembly_language" title="Assembly language">assembly language</a>, originally for the <a href="/wiki/Digital_Equipment_Corporation" title="Digital Equipment Corporation">Digital Equipment Corporation</a> <a href="/wiki/PDP-6" title="PDP-6">PDP-6</a> computer, but the majority of ITS development and use was on the newer, largely <a href="/wiki/Forward_compatibility" title="Forward compatibility">upwards-compatible</a>, <a href="/wiki/PDP-10" title="PDP-10">PDP-10</a>.<sup id="cite_ref-LevyWL_3-2" class="reference"><a href="#cite_note-LevyWL-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> </p><p>Although not used as intensively after about 1986, ITS continued to operate on original hardware at MIT until 1990, and then until 1995 at <a href="/w/index.php?title=Stacken_Computer_Club&action=edit&redlink=1" class="new" title="Stacken Computer Club (page does not exist)">Stacken Computer Club</a><span class="noprint" style="font-size:85%; font-style: normal;"> [<a href="https://sv.wikipedia.org/wiki/Stacken" class="extiw" title="sv:Stacken">sv</a>]</span> in Sweden. Today, some ITS implementations continue to be remotely accessible, via <a href="/wiki/Emulator" title="Emulator">emulation</a> of PDP-10 hardware running on modern, low-cost computers supported by interested hackers. </p> <div class="mw-heading mw-heading2"><h2 id="Significant_technical_features">Significant technical features</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Incompatible_Timesharing_System&action=edit&section=2" title="Edit section: Significant technical features"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>ITS introduced many then-new features: </p> <ul><li>The first <a href="/wiki/Device_independence" class="mw-redirect" title="Device independence">device-independent</a> <a href="/wiki/Graphics_terminal" class="mw-redirect" title="Graphics terminal">graphics terminal</a> output; programs generated generic commands to control screen content, which the system automatically translated into the appropriate character sequences for the particular type of terminal operated by the user.</li> <li>A general mechanism for implementing <a href="/wiki/Virtual_device" title="Virtual device">virtual devices</a> in software running in user processes (which were called "jobs" in ITS).</li> <li>Using the virtual-device mechanism, ITS provided transparent <a href="/wiki/Distributed_file_system" class="mw-redirect" title="Distributed file system">inter-machine filesystem access</a>. The ITS machines were all connected to the <a href="/wiki/ARPANET" title="ARPANET">ARPAnet</a>, and a user on one machine could perform the same operations with files on other ITS machines as if they were local files.</li> <li>Sophisticated <a href="/wiki/Process_management_(computing)" title="Process management (computing)">process management</a>; user processes were organized in a <a href="/wiki/Tree_(data_structure)" class="mw-redirect" title="Tree (data structure)">tree</a>, and a superior process could control a large number of inferior processes. Any inferior process could be frozen at any point in its operation, and its state (including contents of the registers) examined; the process could then be resumed transparently.</li> <li>An advanced <a href="/wiki/Software_interrupt" class="mw-redirect" title="Software interrupt">software interrupt</a> facility that allowed user processes to operate asynchronously, using complex <a href="/wiki/Interrupt_handling" class="mw-redirect" title="Interrupt handling">interrupt handling</a> mechanisms.</li> <li><a href="/wiki/PCLSRing" title="PCLSRing">PCLSRing</a>, a mechanism providing what appeared (to user processes) to be quasi-<a href="/wiki/Atomic_operation" class="mw-redirect" title="Atomic operation">atomic</a>, safely-interruptible <a href="/wiki/System_call" title="System call">system calls</a>. No process could ever observe any process (including itself) in the middle of executing any system call.</li> <li>In support of the AI Lab's robotics work, ITS also supported simultaneous <a href="/wiki/Real-time_computing" title="Real-time computing">real-time</a> and time-sharing operation.</li></ul> <div class="mw-heading mw-heading2"><h2 id="User_environment">User environment</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Incompatible_Timesharing_System&action=edit&section=3" title="Edit section: User environment"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The environment seen by ITS users was philosophically significantly different from that provided by most operating systems at the time.<sup id="cite_ref-LevyWL_3-3" class="reference"><a href="#cite_note-LevyWL-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> </p> <ul><li>Initially there were no <a href="/wiki/Passwords" class="mw-redirect" title="Passwords">passwords</a>, and a user could work on ITS without logging on.<sup id="cite_ref-AIM238_5-0" class="reference"><a href="#cite_note-AIM238-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> Logging on was considered polite, though, so other people knew when one was active on the system.</li> <li>To deal with a rash of incidents where users sought out flaws in the system in order to <a href="/wiki/Crash_(computing)" title="Crash (computing)">crash</a> it, a novel approach was taken. A command which could be run by anyone would cause the system to crash, taking away the challenge and notoriety of doing so. It first also broadcast a message to say who was initiating the crash.</li> <li>All files were editable by all users, including <a href="/wiki/Documentation" title="Documentation">online documentation</a> and <a href="/wiki/Source_code" title="Source code">source code</a>. A series of informal papers and technical notes documented new commands, technical issues, primitive games, mathematical puzzles, and other topics of interest to the ITS hacker community. Some were issued as more formal <a href="/wiki/AI_Memo" title="AI Memo">AI Memos</a>, including the iconic <a href="/wiki/HAKMEM" title="HAKMEM">HAKMEM</a> compendium.</li> <li>All users could talk with <a href="/wiki/Instant_messaging" title="Instant messaging">instant messaging</a> on another's terminal, or they could use a command (SHOUT) to ask all active users for help.</li> <li>Users could <a href="/wiki/Remote_administration" title="Remote administration">see what was happening</a> on another's terminal (using a command called OS for "output spy"). A target of OS could detect and kill it using another command called JEDGAR, named after <a href="/wiki/Federal_Bureau_of_Investigation" title="Federal Bureau of Investigation">FBI</a> Director <a href="/wiki/J._Edgar_Hoover" title="J. Edgar Hoover">J. Edgar Hoover</a>. This facility was later disabled with a <a href="/wiki/Placebo" title="Placebo">placebo</a> command: it appeared as if the remote session was killed, but it was not.<sup id="cite_ref-6" class="reference"><a href="#cite_note-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup></li> <li>Tourists (guest users either at MIT AI Lab terminals, or over the ARPAnet) were tolerated and occasionally invited to actively join the ITS community. Informal policy on tourist access was later formalized in a written policy.<sup id="cite_ref-7" class="reference"><a href="#cite_note-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup> Ease of access, with or without a guest account, allowed interested parties to informally explore and experiment with the operating system, application programs, and <a href="/wiki/Hacker_culture" title="Hacker culture">hacker culture</a>. Working copies of documentation and source code could be freely consulted or updated by anybody on the system.</li> <li>System security, to the extent that it existed, was mostly-based on <a href="/wiki/De_facto" title="De facto">de facto</a> "<a href="/wiki/Security_by_obscurity" class="mw-redirect" title="Security by obscurity">security by obscurity</a>". Guest hackers willing to dedicate significant time and effort to learning ITS were expected to behave respectfully, and to avoid interfering with the research projects which funded the hardware and software systems. There was little of exclusive value on the ITS systems except information, much of which would eventually be published for free distribution, and open and free sharing of knowledge was generally encouraged.</li></ul> <p>The wide-open ITS philosophy and collaborative community were the direct forerunner of the <a href="/wiki/Free_and_open-source_software" title="Free and open-source software">free and open-source software</a> (FOSS), <a href="/wiki/Open-design_movement" title="Open-design movement">open-design</a>, and <a href="/wiki/Wiki" title="Wiki">Wiki</a> movements.<sup id="cite_ref-PanBonk_8-0" class="reference"><a href="#cite_note-PanBonk-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Stallman_9-0" class="reference"><a href="#cite_note-Stallman-9"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-HOSS_10-0" class="reference"><a href="#cite_note-HOSS-10"><span class="cite-bracket">[</span>10<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="Important_applications_developed_on_ITS">Important applications developed on ITS</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Incompatible_Timesharing_System&action=edit&section=4" title="Edit section: Important applications developed on ITS"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The <a href="/wiki/Emacs" title="Emacs">EMACS</a> ("Editor MACroS") editor was originally written on ITS. In its ITS instantiation it was a collection of <a href="/wiki/TECO_(text_editor)" title="TECO (text editor)">TECO</a> programs (called "macros"). On later operating systems, it was written in the common language of those systems – for example, the <a href="/wiki/C_language" class="mw-redirect" title="C language">C language</a> under <a href="/wiki/Unix" title="Unix">Unix</a>, and <a href="/wiki/Zetalisp" class="mw-redirect" title="Zetalisp">Zetalisp</a> under the <a href="/wiki/Lisp_Machine" class="mw-redirect" title="Lisp Machine">Lisp Machine</a> system. </p><p><a href="/wiki/GNU" title="GNU">GNU</a>‘s <a href="/wiki/Info_(Unix)" title="Info (Unix)">info</a> help system was originally an EMACS subsystem, and then was later written as a complete standalone system for Unix-like machines. </p><p>Several important programming languages and systems were developed on ITS, including <a href="/wiki/Maclisp" title="Maclisp">MacLisp</a> (the precursor of Zetalisp and <a href="/wiki/Common_Lisp" title="Common Lisp">Common Lisp</a>), <a href="/wiki/Micro-Planner_(programming_language)" class="mw-redirect" title="Micro-Planner (programming language)">Microplanner</a> (implemented in MacLisp), <a href="/wiki/MDL_programming_language" class="mw-redirect" title="MDL programming language">MDL</a> (which became the basis of <a href="/wiki/Infocom" title="Infocom">Infocom</a>'s programming environment), and <a href="/wiki/Scheme_(programming_language)" title="Scheme (programming language)">Scheme</a>. </p><p>Among other significant and influential software subsystems developed on ITS, the <a href="/wiki/Macsyma" title="Macsyma">Macsyma</a> symbolic algebra system, started in 1968, was the first widely-known mathematical computing environment. It was a forerunner of <a href="/wiki/Maxima_(software)" title="Maxima (software)">Maxima</a>, <a href="/wiki/MATLAB" title="MATLAB">MATLAB</a>, <a href="/wiki/Wolfram_Mathematica" title="Wolfram Mathematica">Wolfram Mathematica</a>, and many other <a href="/wiki/List_of_computer_algebra_systems" title="List of computer algebra systems">computer algebra systems</a>. </p><p><a href="/wiki/Terry_Winograd" title="Terry Winograd">Terry Winograd</a>'s natural-language interpreter <a href="/wiki/SHRDLU" title="SHRDLU">SHRDLU</a> was developed on ITS. The computer game <i><a href="/wiki/Zork" title="Zork">Zork</a></i> was also originally written on ITS.<sup class="noprint Inline-Template Template-Fact" style="white-space:nowrap;">[<i><a href="/wiki/Wikipedia:Citation_needed" title="Wikipedia:Citation needed"><span title="This claim needs references to reliable sources. (February 2025)">citation needed</span></a></i>]</sup> </p><p><a href="/wiki/Richard_Greenblatt_(programmer)" title="Richard Greenblatt (programmer)">Richard Greenblatt</a>'s Mac Hack VI was the top-rated chess program for years<sup class="noprint Inline-Template Template-Fact" style="white-space:nowrap;">[<i><a href="/wiki/Wikipedia:Citation_needed" title="Wikipedia:Citation needed"><span title="This claim needs references to reliable sources. (April 2019)">citation needed</span></a></i>]</sup> and was the first to display a graphical board representation.<sup class="noprint Inline-Template Template-Fact" style="white-space:nowrap;">[<i><a href="/wiki/Wikipedia:Citation_needed" title="Wikipedia:Citation needed"><span title="This claim needs references to reliable sources. (April 2019)">citation needed</span></a></i>]</sup> </p> <div class="mw-heading mw-heading2"><h2 id="Miscellaneous">Miscellaneous</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Incompatible_Timesharing_System&action=edit&section=5" title="Edit section: Miscellaneous"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The default ITS top-level <a href="/wiki/Command_line_interface" class="mw-redirect" title="Command line interface">command interpreter</a> was the PDP-10 machine language debugger (<a href="/wiki/Dynamic_debugging_technique" title="Dynamic debugging technique">DDT</a>). The usual <a href="/wiki/Text_editor" title="Text editor">text editor</a> on ITS was <a href="/wiki/Text_Editor_and_Corrector" class="mw-redirect" title="Text Editor and Corrector">TECO</a> and later <a href="/wiki/Emacs" title="Emacs">Emacs</a>, which was written in TECO. Both DDT and TECO were implemented through simple <a href="/wiki/Dispatch_table" title="Dispatch table">dispatch tables</a> on single-letter commands, and thus had no true <a href="/wiki/Syntax_of_programming_languages" class="mw-redirect" title="Syntax of programming languages">syntax</a>. The ITS <a href="/wiki/Task_manager" title="Task manager">task manager</a> was called PEEK. </p><p>The local spelling "TURIST" is an artifact of six-character filename (and other identifier) limitations, which is traceable to six <a href="/wiki/Sixbit" class="mw-redirect" title="Sixbit">SIXBIT encoded</a> characters fitting into a single 36-bit PDP-10 word. "TURIST" may also have been a <a href="/wiki/Pun" title="Pun">pun</a> on <a href="/wiki/Alan_Turing" title="Alan Turing">Alan Turing</a>, a pioneer of theoretical <a href="/wiki/Computer_science" title="Computer science">computer science</a>.<sup id="cite_ref-Turist_11-0" class="reference"><a href="#cite_note-Turist-11"><span class="cite-bracket">[</span>11<span class="cite-bracket">]</span></a></sup> The less-complimentary term "<a href="/wiki/Luser" title="Luser">LUSER</a>" was also applied to guest users, especially those who repeatedly engaged in clueless or vandalous behavior.<sup id="cite_ref-Luser_12-0" class="reference"><a href="#cite_note-Luser-12"><span class="cite-bracket">[</span>12<span class="cite-bracket">]</span></a></sup> </p><p>The <a href="/wiki/Jargon_File" title="Jargon File">Jargon File</a> started as a combined effort between people on the ITS machines at MIT and at Stanford University <a href="/wiki/Stanford_Artificial_Intelligence_Laboratory" class="mw-redirect" title="Stanford Artificial Intelligence Laboratory">SAIL</a>. The document described much of the terminology, puns, and culture of the two AI Labs and related research groups, and is the direct predecessor of the <i>Hacker's Dictionary</i> (1983),<sup id="cite_ref-TOHD_13-0" class="reference"><a href="#cite_note-TOHD-13"><span class="cite-bracket">[</span>13<span class="cite-bracket">]</span></a></sup> the first compendium of hacker jargon to be issued by a major publisher (<a href="/wiki/MIT_Press" title="MIT Press">MIT Press</a>). </p><p>Different implementations of ITS supported an odd array of peripherals, including an automatic wire stripper devised by hacker Richard Greenblatt, who needed a supply of pre-stripped jumper wires of various lengths for <a href="/wiki/Wire-wrapping" class="mw-redirect" title="Wire-wrapping">wire-wrapping</a> computer hardware he and others were prototyping. The device used a <a href="/wiki/Stepper_motor" title="Stepper motor">stepper motor</a> and a formerly hand-held wire stripper tool and cutter, operated by <a href="/wiki/Solenoid" title="Solenoid">solenoid</a>, all under computer control from ITS software. The device was accessible by any ITS user, but was disappointingly unreliable in actual use. </p><p>The <a href="/w/index.php?title=Xerox_Graphics_Printer&action=edit&redlink=1" class="new" title="Xerox Graphics Printer (page does not exist)">Xerox Graphics Printer</a> (XGP), one of the first laser printers, was supported by ITS by 1974.<sup id="cite_ref-14" class="reference"><a href="#cite_note-14"><span class="cite-bracket">[</span>14<span class="cite-bracket">]</span></a></sup> The MIT AI Lab had one of these prototype continuous roll-fed printers for experimentation and use by its staff. By 1982, the XGP was supplemented by a <a href="/wiki/Xerox_Dover" title="Xerox Dover">Xerox Dover</a> printer, an early sheet-fed laser printer.<sup id="cite_ref-15" class="reference"><a href="#cite_note-15"><span class="cite-bracket">[</span>15<span class="cite-bracket">]</span></a></sup> Although any ITS user could send files to the laser printers, physical access to pick up printouts was limited to staff and others who obtained access to the MIT lab, to control usage of printer supplies which had to be specially ordered. </p><p>CTSS and ITS file systems have a number of design elements in common. Both have an M.F.D. (master file directory) and one or more U.F.D. (user file directories). Neither of them have nested directories (sub-directories) Both have file names consisting of two names which are a maximum of six-characters long. Both support linked files. </p> <div class="mw-heading mw-heading2"><h2 id="Original_developers">Original developers</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Incompatible_Timesharing_System&action=edit&section=6" title="Edit section: Original developers"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a href="/wiki/Richard_Greenblatt_(programmer)" title="Richard Greenblatt (programmer)">Richard Greenblatt</a></li> <li><a href="/wiki/Stewart_Nelson_(hacker)" class="mw-redirect" title="Stewart Nelson (hacker)">Stewart Nelson</a></li> <li><a href="/wiki/Tom_Knight_(scientist)" title="Tom Knight (scientist)">Tom Knight</a></li> <li><a href="/wiki/Richard_Stallman" title="Richard Stallman">Richard Stallman</a></li></ul> <div class="mw-heading mw-heading2"><h2 id="See_also">See also</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Incompatible_Timesharing_System&action=edit&section=7" title="Edit section: See also"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a href="/wiki/Time-sharing_system_evolution" title="Time-sharing system evolution">Time-sharing system evolution</a></li></ul> <div class="mw-heading mw-heading2"><h2 id="References">References</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Incompatible_Timesharing_System&action=edit&section=8" title="Edit section: References"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1239543626">.mw-parser-output .reflist{margin-bottom:0.5em;list-style-type:decimal}@media screen{.mw-parser-output .reflist{font-size:90%}}.mw-parser-output .reflist .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output 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.citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output .id-lock-free.id-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/6/65/Lock-green.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited.id-lock-limited a,.mw-parser-output .id-lock-registration.id-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/d/d6/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription.id-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/a/aa/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-ws-icon a{background:url("//upload.wikimedia.org/wikipedia/commons/4/4c/Wikisource-logo.svg")right 0.1em center/12px no-repeat}body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-free a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-limited a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-registration a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-subscription a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .cs1-ws-icon a{background-size:contain;padding:0 1em 0 0}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;color:var(--color-error,#d33)}.mw-parser-output .cs1-visible-error{color:var(--color-error,#d33)}.mw-parser-output .cs1-maint{display:none;color:#085;margin-left:0.3em}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output .citation .mw-selflink{font-weight:inherit}@media screen{.mw-parser-output .cs1-format{font-size:95%}html.skin-theme-clientpref-night .mw-parser-output .cs1-maint{color:#18911f}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .cs1-maint{color:#18911f}}</style><cite class="citation book cs1"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20160308100743/http://www.dtic.mil/dtic/tr/fulltext/u2/681342.pdf"><i>Project MAC Progress Report IV</i></a> <span class="cs1-format">(PDF)</span>. 1967. p. 18. 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Retrieved <span class="nowrap">2021-08-20</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=MIT+Dspace&rft.atitle=Getting+Started+Computing+at+the+Al+Lab&rft.date=1982-09-07&rft.aulast=Stacy&rft.aufirst=Christopher+C.&rft_id=https%3A%2F%2Fdspace.mit.edu%2Fbitstream%2Fhandle%2F1721.1%2F41180%2FAI_WP_235.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3AIncompatible+Timesharing+System" class="Z3988"></span></span> </li> </ol></div></div> <div class="mw-heading mw-heading3"><h3 id="Bibliography">Bibliography</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Incompatible_Timesharing_System&action=edit&section=9" title="Edit section: Bibliography"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1239549316">.mw-parser-output .refbegin{margin-bottom:0.5em}.mw-parser-output .refbegin-hanging-indents>ul{margin-left:0}.mw-parser-output .refbegin-hanging-indents>ul>li{margin-left:0;padding-left:3.2em;text-indent:-3.2em}.mw-parser-output .refbegin-hanging-indents ul,.mw-parser-output .refbegin-hanging-indents ul li{list-style:none}@media(max-width:720px){.mw-parser-output .refbegin-hanging-indents>ul>li{padding-left:1.6em;text-indent:-1.6em}}.mw-parser-output .refbegin-columns{margin-top:0.3em}.mw-parser-output .refbegin-columns ul{margin-top:0}.mw-parser-output .refbegin-columns li{page-break-inside:avoid;break-inside:avoid-column}@media screen{.mw-parser-output .refbegin{font-size:90%}}</style><div class="refbegin" style=""> <ul><li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFEastlakeGreenblattHollowayKnight1969" class="citation book cs1">Eastlake, D; Greenblatt, R; Holloway, J; Knight, T; Nelson, S (July 1969). <a rel="nofollow" class="external text" href="http://bitsavers.org/pdf/mit/ai/aim/AIM-161A.pdf"><i>ITS Reference Manual, Version 1.5</i></a> <span class="cs1-format">(PDF)</span>. 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Retrieved <span class="nowrap">December 21,</span> 2009</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=PCLSRing%3A+Keeping+Process+State+Modular&rft.date=2000-12-29&rft.aulast=Bawden&rft.aufirst=Alan&rft_id=http%3A%2F%2Ffare.tunes.org%2Ftmp%2Femergent%2Fpclsr.htm&rfr_id=info%3Asid%2Fen.wikipedia.org%3AIncompatible+Timesharing+System" class="Z3988"></span></li> <li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFLin2004" class="citation journal cs1">Lin, Yuwei (February 24, 2004). <a rel="nofollow" class="external text" href="http://ubiquity.acm.org/article.cfm?id=985611">"Epistemologically Multiple Actor-Centered Systems: or, EMACS At Work"</a>. <i>Ubiquity</i>. <b>5</b> (1). <a href="/wiki/Association_for_Computing_Machinery" title="Association for Computing Machinery">Association for Computing Machinery</a><span class="reference-accessdate">. Retrieved <span class="nowrap">December 21,</span> 2009</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Ubiquity&rft.atitle=Epistemologically+Multiple+Actor-Centered+Systems%3A+or%2C+EMACS+At+Work&rft.volume=5&rft.issue=1&rft.date=2004-02-24&rft.aulast=Lin&rft.aufirst=Yuwei&rft_id=http%3A%2F%2Fubiquity.acm.org%2Farticle.cfm%3Fid%3D985611&rfr_id=info%3Asid%2Fen.wikipedia.org%3AIncompatible+Timesharing+System" class="Z3988"></span></li> <li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFChiouMusicSpragueWahba2001" class="citation web cs1">Chiou, Stefanie; Music, Craig; Sprague, Kara; Wahba, Rebekah (December 16, 2001). <a rel="nofollow" class="external text" href="https://web.archive.org/web/20110514101306/http://mit.edu/6.933/www/Fall2001/AILab.pdf">"A Marriage of Convenience: The Founding of the MIT Artificial Intelligence Laboratory"</a> <span class="cs1-format">(PDF)</span>. Archived from <a rel="nofollow" class="external text" href="http://mit.edu/6.933/www/Fall2001/AILab.pdf">the original</a> <span class="cs1-format">(PDF)</span> on May 14, 2011<span class="reference-accessdate">. Retrieved <span class="nowrap">December 21,</span> 2009</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=A+Marriage+of+Convenience%3A+The+Founding+of+the+MIT+Artificial+Intelligence+Laboratory&rft.date=2001-12-16&rft.aulast=Chiou&rft.aufirst=Stefanie&rft.au=Music%2C+Craig&rft.au=Sprague%2C+Kara&rft.au=Wahba%2C+Rebekah&rft_id=http%3A%2F%2Fmit.edu%2F6.933%2Fwww%2FFall2001%2FAILab.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3AIncompatible+Timesharing+System" class="Z3988"></span></li> <li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFWilliams2002" class="citation book cs1">Williams, Sam (2002). <span class="id-lock-registration" title="Free registration required"><a rel="nofollow" class="external text" href="https://archive.org/details/freeasinfreedomr00will"><i>Free as in Freedom: Richard Stallman's Crusade for Free Software</i></a></span>. Petaluma, CA: <a href="/wiki/O%27Reilly_Media" title="O'Reilly Media">O'Reilly</a>. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-0-596-00287-9" title="Special:BookSources/978-0-596-00287-9"><bdi>978-0-596-00287-9</bdi></a><span class="reference-accessdate">. Retrieved <span class="nowrap">December 21,</span> 2009</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Free+as+in+Freedom%3A+Richard+Stallman%27s+Crusade+for+Free+Software&rft.place=Petaluma%2C+CA&rft.pub=O%27Reilly&rft.date=2002&rft.isbn=978-0-596-00287-9&rft.aulast=Williams&rft.aufirst=Sam&rft_id=https%3A%2F%2Farchive.org%2Fdetails%2Ffreeasinfreedomr00will&rfr_id=info%3Asid%2Fen.wikipedia.org%3AIncompatible+Timesharing+System" class="Z3988"></span></li></ul> </div> <div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Incompatible_Timesharing_System&action=edit&section=10" title="Edit section: External links"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a rel="nofollow" class="external text" href="https://web.archive.org/web/20120226113808/http://www.avanthar.com/~healyzh/sysdoc/sysdoc.html">ITS System Documentation</a></li> <li><a rel="nofollow" class="external text" href="http://its.svensson.org/">SV: An ITS system running online and open for logins</a></li> <li><a rel="nofollow" class="external text" href="http://up.update.uu.se/">UP: Public ITS system operated by the Update Computer Club at Uppsala University</a></li> <li><a rel="nofollow" class="external text" href="http://klh10.trailing-edge.com/">KLH10: Ken Harrenstien's PDP-10 emulator</a></li> <li><a rel="nofollow" class="external text" href="https://web.archive.org/web/20070826152708/http://www.cosmic.com/u/mirian/its/itsbuild.html">instructions allowing ITS to run</a> on the <a href="/wiki/SIMH" title="SIMH">SIMH</a> <a href="/wiki/PDP-10" title="PDP-10">PDP-10</a> emulator.</li> <li><a rel="nofollow" class="external text" href="http://catb.org/~esr/jargon/html/I/ITS.html">Jargon File Entry</a></li> <li><a rel="nofollow" class="external text" href="https://web.archive.org/web/20110726144837/http://www.stswiki.org/index.php?title=Incompatible_Timesharing_System_bibliography">ITS bibliography</a></li></ul> <div class="navbox-styles"><style data-mw-deduplicate="TemplateStyles:r1129693374">.mw-parser-output .hlist dl,.mw-parser-output .hlist ol,.mw-parser-output .hlist ul{margin:0;padding:0}.mw-parser-output .hlist dd,.mw-parser-output .hlist dt,.mw-parser-output .hlist li{margin:0;display:inline}.mw-parser-output .hlist.inline,.mw-parser-output .hlist.inline dl,.mw-parser-output .hlist.inline ol,.mw-parser-output .hlist.inline ul,.mw-parser-output .hlist dl dl,.mw-parser-output .hlist dl ol,.mw-parser-output .hlist dl ul,.mw-parser-output .hlist ol dl,.mw-parser-output .hlist ol ol,.mw-parser-output .hlist ol ul,.mw-parser-output .hlist ul dl,.mw-parser-output .hlist ul ol,.mw-parser-output .hlist ul ul{display:inline}.mw-parser-output .hlist .mw-empty-li{display:none}.mw-parser-output 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