<story><title>Simulating the IBM 360/50 mainframe from its microcode</title><url>https://www.righto.com/2022/01/ibm360model50.html</url></story><parent_chain></parent_chain><comment><author>BXLE_1-1-BitIs1</author><text>One of the stories I heard about the 50 is that if you threw it into the ocean it would sink intermittently.&lt;p&gt;Anyway the 50 was the first computer I was paid to program on. Many were bought to run in 7070 emulator mode as the 50 was the smallest &amp;#x2F; cheapest machine that could run 7070.&lt;p&gt;Happily I was on the 360 side.&lt;p&gt;At another shop, we had 2 50s, one running DOS and the other OS with HASP.&lt;p&gt;One day a student was having trouble with the Test and Set (superceded by Compare and Swap) instruction not setting the condition code properly. I wrote a short diagnostic program to exercise TS, store the resulting condition codes and dump. The instruction was not performing correctly.&lt;p&gt;I showed the dump to the non IBM engineers who hemmed and hawed. A couple days later one phoned me up to say that TS wasn&amp;#x27;t setting the condition code correctly - exactly what I had been telling him.&lt;p&gt;They fixed the problem. The next day I got a phone call that HASP wasn&amp;#x27;t starting on the other 50. Took a dump and found HASP was in a wait just after TS.&lt;p&gt;The engineers had swapped microcode cards between the two machines.&lt;p&gt;My manager was not pleased with the engineers.</text></comment>
<story><title>Simulating the IBM 360/50 mainframe from its microcode</title><url>https://www.righto.com/2022/01/ibm360model50.html</url></story><parent_chain></parent_chain><comment><author>r2sk5t</author><text>Thanks for the blog post @picture. I worked on emulating the 360&amp;#x2F;370 instruction set using both an 8086 processor and a bit slice processor, when I was at Big Blue. The hardware and microcode development was insanely complex. This ended up being a shipped product called the XT and AT&amp;#x2F;370. &lt;a href=&quot;https:&amp;#x2F;&amp;#x2F;en.wikipedia.org&amp;#x2F;wiki&amp;#x2F;PC-based_IBM_mainframe-compatible_systems&quot; rel=&quot;nofollow&quot;&gt;https:&amp;#x2F;&amp;#x2F;en.wikipedia.org&amp;#x2F;wiki&amp;#x2F;PC-based_IBM_mainframe-compati...&lt;/a&gt;</text></comment>