System360 Hardwired vs. Microcoded 401

When I was in school (late 70s) we used a 360-44, and I studied it quite a bit. The 44 had transistorized registers, instead of registers made from core memory as the other models did at the time. It was also (mostly) hard-wired rather than microcoded.

The 44 didn't implement the entire 360 instruction set. The subset implemented was oriented towards scientific computing; all of the 6 byte long instructions were unimplemented. These instructions included decimal arithmetic and memory-to-memory moves. Bottom line was that it was a super Fortran computer and a lousy COBOL computer.

I called the 44 "mostly" hardwired because it had hardware provisions for running an "emulator" to implement te missing instructions. The front console had the standard "Initial Program Load" (modern translation: "boot") button, as well as a 44-specific "Emulator Load" button. We had a magic card deck, kept in a locked drawer, that contained the "Dublin Emulator" that completed te instruction set. After any power down we had to boot the emulator, and then could boot the OS.

I spent some time with the 44 Principles Of Operations manual. The "emulator" ran in what was referred to as the "negative address space" to be flagged, due to an illegal opcode, rather than loading the program new PSW as a 360 normally would it instead flipped to the "negative address space" to give the emulator a chance at it. I only vaguely remember any other details, but it was truly wacky.

...Sam

(Naturally, by the time I saw it, it was being used primarily by undergraduate COBOL clbuttes. AACK.)