IBM System/370 Model 145

<h2 id="virtual-memory">Virtual memory</h2>
Initially, the System/370 Model 145 did not support virtual memory.
Unlike the earlier Model 155 and 165 systems, for which an upgrade to <a href="/facts/Virtual_memory/Lw2GemF5">virtual memory</a> required the purchase of an expensive upgrade to add a DAT box,<a class="footnote-ref" id="fnref:6" href="#fn:6">6</a> the Model 145 already included an associative memory<a class="footnote-ref" id="fnref:7" href="#fn:7">7</a><a class="footnote-ref" id="fnref:8" href="#fn:8">8</a>: CPU 117-CPU 129  used by the <a href="/facts/Microcode/XQEsr2X3">microcode</a> for the DOS compatibility feature from its first shipments in June 1971;<a class="footnote-ref" id="fnref:9" href="#fn:9">9</a> the same hardware was used by the microcode for DAT.<a class="footnote-ref" id="fnref:10" href="#fn:10">10</a>: CPU 139  Although IBM famously chose to exclude virtual storage from the S/370 announcement, that decision was being reconsidered during the completion of the 145 engineering, partly because of virtual memory experience at CSC and elsewhere. The 145 microcode architecture simplified the addition of virtual storage, allowing this capability to be present in early 145s without the extensive hardware modifications needed in other models. However, IBM did not document the 145's virtual storage capability, nor annotate the relevant bits in the control registers and PSW that were displayed on the operator control panel when selected using the roller switches. The Reference and Change bits of the Storage-protection Keys, however, were labeled on the rollers, a dead giveaway to anyone who had worked with the earlier 360/67. Existing S/370-145 customers were happy to learn that they did not have to purchase a hardware upgrade in order to run DOS/VS or OS/VS1 (or OS/VS2 Release 1 – which was possible, but not common because of the limited amount of main storage available on the S/370-145).
This resulted in two advantages of the 145 over the 155 and 165:

<ul><li>370/145 customers did not have to wait as long for this lack of virtual memory to be remedied<a class="footnote-ref" id="fnref:11" href="#fn:11">11</a></li>
<li>there was no need to buy extra hardware: An upgrade to the 145's <a href="/facts/Microcode/XQEsr2X3">microcode</a> through a new microcode floppy disk<a class="footnote-ref" id="fnref:12" href="#fn:12">12</a> enabled virtual memory capability.</li></ul>
<h3>Operating systems</h3>
The 370/145 supported both <a href="/facts/DOS/360_and_successors/bT9PzVHd">DOS/360</a> and <a href="/facts/OS/360_and_successors/nQbdNbx6">OS/360</a>.<a class="footnote-ref" id="fnref:13" href="#fn:13">13</a> Lacking virtual memory support, the 145, as announced, could not run a virtual memory operating system.
Upon gaining virtual memory capability via a microcode update, the 145 could now support the <a href="/facts/VM_(operating_system)/Ymu9SRtX">VMF (Virtual Machine Facility)</a> and <a href="/facts/Conversational_Monitor_System/qmWXRkQT">VM/CMS</a>, a <a href="/facts/Time-sharing/LE5XT9Go">time-sharing</a> system.

<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/List_of_IBM_products/1Dapb82x">List of IBM products</a></li>
<li><a href="/facts/IBM_System/360/7znvpy4K">IBM System/360</a></li>
<li><a href="/facts/IBM_System/370/TRo1jaFw">IBM System/370</a></li></ul>
<h2 id="notes">Notes</h2>

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

<ol>
<li id="fn:1">"System/370 Model 145". IBM Archives. IBM. 23 January 2003. Archived from the original on 2023-07-29. <a href="https://web.archive.org/web/20230729090334/https://www.ibm.com/ibm/history/exhibits/mainframe/mainframe_PP3145.html" target="_blank">https://web.archive.org/web/20230729090334/https://www.ibm.com/ibm/history/exhibits/mainframe/mainframe_PP3145.html</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></li>
<li id="fn:2">"System/370 Model 165". IBM Archives. IBM. 23 January 2003. Archived from the original on 2023-07-29. <a href="https://web.archive.org/web/20230729090329/https://www.ibm.com/ibm/history/exhibits/mainframe/mainframe_PP3165.html" target="_blank">https://web.archive.org/web/20230729090329/https://www.ibm.com/ibm/history/exhibits/mainframe/mainframe_PP3165.html</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></li>
<li id="fn:3">A third 370, the 370/195, had separately been announced the same day as the 155 & 165.[3] <a href="#fnref:3" class="footnote-back-ref">↩</a></li>
<li id="fn:4">William D. Smith (September 24, 1970). "A new computer unveiled by I.B.M". The New York Times. <a href="https://www.nytimes.com/1970/09/24/archives/a-new-computer-unveiled-by-ibm-main-memory-system-uses.html" target="_blank">https://www.nytimes.com/1970/09/24/archives/a-new-computer-unveiled-by-ibm-main-memory-system-uses.html</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></li>
<li id="fn:5">"System/370 Model 145". IBM Archives. IBM. 23 January 2003. Archived from the original on 2023-07-29. <a href="https://web.archive.org/web/20230729090334/https://www.ibm.com/ibm/history/exhibits/mainframe/mainframe_PP3145.html" target="_blank">https://web.archive.org/web/20230729090334/https://www.ibm.com/ibm/history/exhibits/mainframe/mainframe_PP3145.html</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></li>
<li id="fn:6">"What Course for the 3081?". Computerworld. November 24, 1980. p. 34. <a href="https://books.google.com/books?id=cKmJJd7R8PIC&pg=PA34" target="_blank">https://books.google.com/books?id=cKmJJd7R8PIC&pg=PA34</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></li>
<li id="fn:7">IBM Maintenance Library 3145 Processing Unit Theory - Maintenance (PDF) (Second ed.). IBM. October 1971. pp. CPU 117–129. SY24-3581-1. <a href="http://www.bitsavers.org/pdf/ibm/370/fe/3145/SY24-3581-1_3145_Processing_Unit_Theory-Maintenance_Oct71.pdf" target="_blank">http://www.bitsavers.org/pdf/ibm/370/fe/3145/SY24-3581-1_3145_Processing_Unit_Theory-Maintenance_Oct71.pdf</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></li>
<li id="fn:8">IBM Maintenance Library 3145 Processing Unit Theory - Maintenance (PDF) (Fifth ed.). IBM. SY24-3581-4. <a href="http://www.bitsavers.org/pdf/ibm/370/fe/3145/SY24-3581-4_3145_Processor_Theory_Maintenance.pdf" target="_blank">http://www.bitsavers.org/pdf/ibm/370/fe/3145/SY24-3581-4_3145_Processor_Theory_Maintenance.pdf</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></li>
<li id="fn:9">IBM Maintenance Library 3145 Processing Unit Theory - Maintenance (PDF) (Second ed.). IBM. October 1971. pp. CPU 117–129. SY24-3581-1. <a href="http://www.bitsavers.org/pdf/ibm/370/fe/3145/SY24-3581-1_3145_Processing_Unit_Theory-Maintenance_Oct71.pdf" target="_blank">http://www.bitsavers.org/pdf/ibm/370/fe/3145/SY24-3581-1_3145_Processing_Unit_Theory-Maintenance_Oct71.pdf</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></li>
<li id="fn:10">IBM Maintenance Library 3145 Processing Unit Theory - Maintenance (PDF) (Fifth ed.). IBM. SY24-3581-4. <a href="http://www.bitsavers.org/pdf/ibm/370/fe/3145/SY24-3581-4_3145_Processor_Theory_Maintenance.pdf" target="_blank">http://www.bitsavers.org/pdf/ibm/370/fe/3145/SY24-3581-4_3145_Processor_Theory_Maintenance.pdf</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></li>
<li id="fn:11">June 1971 vs. Aug. 1972 <a href="#fnref:11" class="footnote-back-ref">↩</a></li>
<li id="fn:12">IBM Maintenance Library 3145 Processing Unit Theory - Maintenance. IBM. pp. CPU 117–129. SY24-3581-2 <a href="#fnref:12" class="footnote-back-ref">↩</a></li>
<li id="fn:13">"System/370 Model 145". IBM Archives. IBM. 23 January 2003. Archived from the original on 2023-07-29. <a href="https://web.archive.org/web/20230729090334/https://www.ibm.com/ibm/history/exhibits/mainframe/mainframe_PP3145.html" target="_blank">https://web.archive.org/web/20230729090334/https://www.ibm.com/ibm/history/exhibits/mainframe/mainframe_PP3145.html</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></li>
</ol>

IBM System/370 Model 145 open-in-new

IBM System/370 Model 145