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From: mat@amdahl.UUCP (Mike Taylor)
Newsgroups: net.arch
Subject: Re: Re: Apple's new Cray
Message-ID: <2897@amdahl.UUCP>
Date: Mon, 10-Mar-86 11:55:31 EST
Article-I.D.: amdahl.2897
Posted: Mon Mar 10 11:55:31 1986
Date-Received: Wed, 12-Mar-86 22:19:22 EST
References: <562@hoptoad.UUCP> <2900005@ztivax.UUCP>
Organization: Amdahl Corp, Sunnyvale CA
Lines: 26

In article <2900005@ztivax.UUCP>, david@ztivax.UUCP writes:
> /* Written  2:20 am  Mar  1, 1986 by LOGIN@amdahl in ztivax:net.arch */
> In article <562@hoptoad.uucp>, gnu@hoptoad.uucp (John Gilmore) writes:
> >> They apparently believe a Cray running full tilt can emulate e.g. a Mac
> >> and run at about the same speed as the micro would.  Plus have much better
> >> debugging facilities.
> > 
> >A Cray probably isn't fast enough to run at the same speed as the
> >target machine, if you are actually doing logic simulation.
> The Cray may well be useful for what they have in mind.
> those clock frequencies everyone talks so losely about in
> micro-programmed micro's don't equate to instruction speed.  A 10MHz
> 68000 really can only do limited instruction mixes at 1MIP, not
> 10MIPS.  Therefore, they can (using your estimates) do about 200
> instructions per target instruction.  Might be enough.
> Also, the Nanodata QM-1 (or boat_anchor-1) could just about emulate an
> 8080 in real-time, and that was using stone age (1970) technology.

The difference is logic simulation vs. simple emulation.  Logic simulation
is sensitive to the number of cycles (it doesn't "know" about instructions,
just about gates and clocks, etc.). Simple emulation can usually be done,
as you indicate, at about a 40:1 to 60:1 execution time ratio.
-- 
Mike Taylor                        ...!{ihnp4,hplabs,amd,sun}!amdahl!mat

[ This may not reflect my opinion, let alone anyone else's.  ]