Which Dec Emulation is the MOST useful and Versatile?

Paul Koning paulkoning at comcast.net
Sun Oct 29 07:42:16 CDT 2017

> 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. 

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.

> Anything you run on your x86 (or ARM, MIPS, SPARC, Alpha, etc) does not
> meet that definition, and is a simulator, since those processors have only
> general-purpose hardware and microcode.
> Lots of people have other definitions of "emulator" which they've just
> pulled out of their a**, but since the System/360 architects invented it, I
> see no good reason to prefer anyone else's definition.

"emulation" is just a standard English word.  I don't see a good reason to limit its application here to a specific intepretation given to it in a particular IBM product.  It's not as if IBM's terminology is necessarily the predominant one in IT (consider "data set").  And in particular, as was pointed out before, "emulator" has a quite specific (and different) meaning in the 1980s through 2000 or so in microprocessor development hardware.


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