Edinburgh Multiple Access System

<h2 id="history">History</h2>
Originally running on the <a href="/facts/ICL_System_4%2f75/3deHpWzN">ICL System 4/75</a> mainframe (based on the design of the <a href="/facts/IBM_360/7znvpy4K">IBM 360</a>) it was later reimplemented <a class="footnote-ref" id="fnref:2" href="#fn:2">2</a><a class="footnote-ref" id="fnref:3" href="#fn:3">3</a><a class="footnote-ref" id="fnref:4" href="#fn:4">4</a> on the <a href="/facts/ICL_2900/ka6K2NFC">ICL 2900 series of mainframes</a> (as EMAS 2900 or EMAS-2) where it ran in service until the mid-1980s. Near the end of its life, the refactored version was back-ported (as EMAS-3) to the <a href="/facts/Amdahl_Corporation/oCbmoP1z">Amdahl</a> 470 mainframe clone, and thence to the IBM <a href="/facts/System%2f370-XA/TRo1jaFw">System/370-XA</a> architecture (the latter with help from the <a href="/facts/University_of_Kent/NrM11NIL">University of Kent</a>, although they never actually ran EMAS-3). The <a href="/facts/Hitachi_Data_Systems/qYvQecjX">National Advanced System</a> (NAS) VL80 IBM mainframe clone followed later. The final EMAS system (the Edinburgh VL80) was decommissioned in July 1992.
The <a href="/facts/University_of_Kent/NrM11NIL">University of Kent</a> system went live in December 1979, and ran on the least powerful machine in the <a href="/facts/ICL_2900/ka6K2NFC">ICL 2900</a> range - an ICL 2960, with 2 MB of memory, executing about 290k instructions per second. Despite this, it reliably supported around 30 users. This number increased in 1983 with the addition of an additional 2 MB of memory and a second Order Code Processor (OCP) (what is normally known as a CPU) running with <a href="/facts/Symmetric_multiprocessing/T9CahUsN">symmetric multiprocessing</a>. This system was decommissioned in August 1986.

<h2 id="features">Features</h2>
EMAS was written entirely in the <a href="/facts/Edinburgh_IMP/9REjMKsE">Edinburgh IMP</a> <a href="/facts/Programming_language/cWTYbgWa">programming language</a>, with only a small number of critical functions using embedded assembler within IMP sources. It had several features that were advanced for the time, including <a href="/facts/Dynamic_linking/4vQ2J2xS">dynamic linking</a>,<a class="footnote-ref" id="fnref:5" href="#fn:5">5</a> multi-level storage, an efficient <a href="/facts/Scheduling_(computing)/XptmcM1a">scheduler</a>,<a class="footnote-ref" id="fnref:6" href="#fn:6">6</a> a separate user-space <a href="/facts/Kernel_(operating_system)/uEj4U3Rz">kernel</a> ('director'),<a class="footnote-ref" id="fnref:7" href="#fn:7">7</a> a user-level <a href="/facts/Shell_(computing)/Sa67elS7">shell</a> ('basic command interpreter'),<a class="footnote-ref" id="fnref:8" href="#fn:8">8</a> a comprehensive archiving system<a class="footnote-ref" id="fnref:9" href="#fn:9">9</a> and a <a href="/facts/Memory-mapped_file/veYrNQnl">memory-mapped file</a> architecture.
Such features led EMAS supporters to claim that their system was superior to <a href="/facts/Unix/0pNL2seI">Unix</a> for the first 20 years of the latter's existence.

<h2 id="legacy">Legacy</h2>
The Edinburgh Computer History Project is attempting to salvage some of the lessons learned<a class="footnote-ref" id="fnref:10" href="#fn:10">10</a> from the EMAS project and has the complete source code of EMAS online for public browsing.<a class="footnote-ref" id="fnref:11" href="#fn:11">11</a>

<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/Atlas_Autocode/M2bAR9hu">Atlas Autocode</a></li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1">Whitfield, H.; Wight, A. S. (1 January 1973). "EMAS—The Edinburgh Multi-Access System". The Computer Journal. 16 (4): 331–346. doi:10.1093/comjnl/16.4.331. <a href="https://doi.org/10.1093%2Fcomjnl%2F16.4.331" target="_blank">https://doi.org/10.1093%2Fcomjnl%2F16.4.331</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></li>
<li id="fn:2">"Archived copy". Archived from the original on 16 December 2004. Retrieved 9 October 2004.{{cite web}}: CS1 maint: archived copy as title (link) <a href="https://web.archive.org/web/20041216160948/http://www.gtoal.com/athome/edinburgh/docs/Experiment/again.html" target="_blank">https://web.archive.org/web/20041216160948/http://www.gtoal.com/athome/edinburgh/docs/Experiment/again.html</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></li>
<li id="fn:3">Stephens, P. D. (1980). "The evolution of the operating system EMAS 2900". Software: Practice and Experience. 10 (12): 993–1008. doi:10.1002/spe.4380101206. S2CID 31830708. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></li>
<li id="fn:4">Rees, D. J. (1982). "The kernel of the EMAS 2900 operating system". Software: Practice and Experience. 12 (7): 655–667. doi:10.1002/spe.4380120707. S2CID 22177787. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></li>
<li id="fn:5">"Index of /archive/os/emas/emas2/subsystem/doc/loader". history.dcs.ed.ac.uk. <a href="http://history.dcs.ed.ac.uk/archive/os/emas/emas2/subsystem/doc/loader/" target="_blank">http://history.dcs.ed.ac.uk/archive/os/emas/emas2/subsystem/doc/loader/</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></li>
<li id="fn:6">Shelness, N. H. (1974). "The Edinburgh Multi-Access System scheduling and allocation procedures in the resident supervisor". Operating Systems. Lecture Notes in Computer Science. Vol. 16. pp. 293–310. doi:10.1007/BFb0029366. ISBN 978-3-540-06849-5. <a href="978-3-540-06849-5" target="_blank">978-3-540-06849-5</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></li>
<li id="fn:7">Rees, D. J. (1 January 1975). "The EMAS Director". The Computer Journal. 18 (2): 122–130. doi:10.1093/comjnl/18.2.122. <a href="https://doi.org/10.1093%2Fcomjnl%2F18.2.122" target="_blank">https://doi.org/10.1093%2Fcomjnl%2F18.2.122</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></li>
<li id="fn:8">Millard, G. E.; Rees, D. J.; Whitfield, H. (1 January 1975). "The standard EMAS subsystem". The Computer Journal. 18 (3): 213–219. doi:10.1093/comjnl/18.3.213. <a href="https://doi.org/10.1093%2Fcomjnl%2F18.3.213" target="_blank">https://doi.org/10.1093%2Fcomjnl%2F18.3.213</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></li>
<li id="fn:9">Wight, A. S. (1 January 1975). "The EMAS Archiving Program". The Computer Journal. 18 (2): 131–134. doi:10.1093/comjnl/18.2.131. <a href="https://doi.org/10.1093%2Fcomjnl%2F18.2.131" target="_blank">https://doi.org/10.1093%2Fcomjnl%2F18.2.131</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></li>
<li id="fn:10">Forsyth, C. H. (2011). "More Taste: Less Greed?". history.dcs.ed.ac.uk. Department of Computer Science University of York. <a href="https://history.dcs.ed.ac.uk/archive/os/emas/docs/taste/" target="_blank">https://history.dcs.ed.ac.uk/archive/os/emas/docs/taste/</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></li>
<li id="fn:11">"Index of /archive/os/emas". history.dcs.ed.ac.uk. <a href="http://history.dcs.ed.ac.uk/archive/os/emas/" target="_blank">http://history.dcs.ed.ac.uk/archive/os/emas/</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></li>
</ol>

Edinburgh Multiple Access System open-in-new

Edinburgh Multiple Access System