by steve-myers » Fri Dec 31, 2010 12:00 pm
Historically, there have been many emulators around that do various things. How many? I don't know and will not speculate. Emulators can be in both hardware and software.
There was a mostly forgotten (now) package to emulate System/360 on 709x.
I think there were several emulators for various things on IBM 1130. I'm pretty sure there was a 1620 emulator for the 1130, but I don't know the details very well.
Early in System/360 there were emulators for 14xx second generation equipment using emulation in hardware. These were pretty poor stuff. You used the entire System/360 to emulate the 14xx machine. The 14xx emulators were on lower end System/360 models like the Model 30 and Model 40.
System/360 Model 65 could emulate higher end second generation machines like the 709x or the 7080. As with 14xx emulation, this emulation ran standalone.
In the early 1970s I encountered a software only emulation of 14xx machines that ran as a job step on System/370 machines.
In addition, System/370 Model 165 and Model 168 offered emulation of 7080 or 709x. These emulations required hardware assists, but ran as job steps in OS/360, OS/VS2 Release 1 and MVS so a single job could intermix emulation and much more efficient System/360 functions like sorting in a single job. There was also a hardware feature for some System/370 models that allowed DOS/360 to run inside OS/360, OS/VS2 Rel 1 or MVS.
In emulation we cannot forget Operating Systems like CP/67 on System/360 Model 67. One of the original ideas was to "emulate" regular System/360 machines, though sometimes with larger defined storage emulated using virtual memory. I believe some users found it was better to run multiple OS/360 PCP systems in CP/67 than to run the same workload under OS/360 MFT or MVT. Later it was altered to "emulate" CP/67 itself to allow new versions of CP/67 to be tested under a production CP/67, though the emulated system suffered a large performance "hit." Still later it was used to "emulate" first version System/370 systems. CP/67 was so successful IBM turned it into a fully supported product called VM/370 when second generation System/370 with virtual memory appeared.
Now we have emulation products for PC type equipment like PC/370 and Hercules that emulate Z series mainframe systems, as well as System/370 equipment types that are not provided on Z series systems. You can IPL OS/360 in Hercules, which cannot be done on real Z series machines.