Which Dec Emulation is the MOST useful and Versatile?

Jon Elson elson at pico-systems.com
Sun Oct 29 12:43:29 CDT 2017

On 10/29/2017 07:42 AM, Paul Koning via cctalk wrote:
>> On Oct 28, 2017, at 10:09 PM, Eric Smith via cctech <cctech at classiccmp.org> wrote:
>> IBM invented computer emulation and introduced it with System/360 in 1964.
>> They defined it as using special-purpose hardware and/or microcode on a
>> computer to simulate a different computer.
> That's certainly a successful early commercial implementation of emulation, done using a particular implementation approach.  At least for some of the emulator features -- I believe you're talking about the 1401 emulator.  IBM didn't use that all the time; the emulator feature in the 360 model 44, to emlulate the missing instructions, uses standard 360 code.
Except for certain machines (360/44, 360/91-95 series, model 
195) all other 360's were also emulated by microcode.
there really was no difference in running 360 code or 1401 
code on a 360 system, they were both done by microcode 

The 360/44 had no control store, so any emulation/simulation 
had to be done by a program written in 360 instructions.
The 360/44 was a hardwired 360.  Note that while the 360 was 
a 32-bit instruction set, the 360/30 had only an 8-bit data 
path, and the 360/40 had only a 16-bit data path.
> It's not clear if that IBM product amounts to inventing emulation.  It seems likely there are earlier ones, possibly not with that particular choice of implementation techniques.
Yes, there were others.  Burroughs and Univac also used 
microcode at about the same time.  I'm not sure the original 
DEC PDP-10 (KA-10) used microcode, but the KI-10 did.


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