Another limited machine was the 360 model 44, which omitted the string and decimal instructions. So it couldn't run OS/360; it had its own operating system (PS/44?). But there was a fix for that: an optional "emulation" feature would add a separate chunk of memory in which an instruction emulation library would run that would simulate the missing instructions. Think of it like the full VAX instruction emulation done in some microVAX models. It's a very obscure feature; I've looked for descriptions but not found much at all. Our 360/44 in college had this, and as a result, it did run OS/360 (19.6 PCP). And it ran PL/I applications -- VERY slowly. The emulator was loaded from a binary card deck, only if needed (core memory -- it wasn't normally done). It was an interesting bit of magic; the actual load was done by a complex channel program, which would actually pick apart the fields of the object deck to extract the load address and length fields of each binary card, modify the channel program from those fields, then read the data portion of the card into the correct location. A pretty impressive combination of command and data chaining. paul