[cctalk] Re: IBM 360 and 1400 series emulation

Um, what? In college I used a 360/44, which ran OS/360 (PCP 19.6, all that could fit in 128 kB of memory), which was made possible by the fact that it had the "emulator" option. But that wasn't a 1620 emulation; instead, it added the SS instructions of the standard 360 instruction set back in, those were omitted from the base model 44. Without SS instructions, OS/360 could not run, which is why the model 44 had an operating system specifically for that machine (PS/44 ? I'm not sure, I never used it). The emulator had a separate chunk of memory and a separate IPL button; unimplemented instructions would trap to that memory for the emulator to handle -- very much like how subset VAX systems like MicroVAX would emulate the missing instructions. The emulator binary came in a card deck, a standard BPS binary deck preceded by a single-card loader that was an amazingly clever self-modifying channel program. The entire logic to interpret the fields of the binary cards and load the entire deck to the right places was implemented in that one-card channel program. I read the relevant documentation back then and decoded the loader, but I have never seen any of it since; even just a bare mention of the emulator feature is nearly non-existent. paul