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From: bzs@bu-cs.BU.EDU (Barry Shein)
Newsgroups: comp.edu
Subject: Re: portable code
Message-ID: <2796@bu-cs.BU.EDU>
Date: Fri, 5-Dec-86 00:53:32 EST
Article-I.D.: bu-cs.2796
Posted: Fri Dec  5 00:53:32 1986
Date-Received: Fri, 5-Dec-86 05:55:27 EST
Organization: Boston U. Comp. Sci.
Lines: 33


>Hardly.  I don't know what MIS shop you work in, but if the hardware
>didn't change underneath there wouldn't be any need for autocoder or
>VM.  The main reason VM is a product from IBM is so that MVS can be run
>on the newer/faster CPU's.
>
>-Ron

Huh? Most shops don't run MVS on top of VM, especially on the newer/faster
CPUs for two reasons:

	1. It's a performance hit, not much, but 10% (which I think
	is a fair estimate) of an $8M 3090 is significant.

	2. VM won't support MVS/XA (extended architecture), or at least
	not yet, or at least not recently, I know XA support in VM
	is promised but for years it wasn't available.

VM basically supports a machine environment (such as trapping and
emulating all priv'd instructions), not the architecture, all non-priv
instructions (give or take memory accesses) run on the raw machine even
under VM.

IBM keeps implementing the 370 architecture on different hardware (and
also did so with the 360 architecture) but VM does little if anything
(I am sure there are nits to pick here) to bridge the difference, that's
below VM.

But yes, there are at least two versions of UNIX which run under VM,
IX/370 from IBM and AMDAHL/AT&T/UTS.


	-Barry Shein, Boston University