Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!mhuxt!houxm!whuxl!whuxlm!akgua!gatech!seismo!mcvax!unido!ztivax!david
From: david@ztivax.UUCP
Newsgroups: net.arch
Subject: Re: Re: Apple's new Cray
Message-ID: <2900005@ztivax.UUCP>
Date: Thu, 6-Mar-86 15:46:00 EST
Article-I.D.: ztivax.2900005
Posted: Thu Mar  6 15:46:00 1986
Date-Received: Sun, 9-Mar-86 08:38:17 EST
References: <562@hoptoad.UUCP>
Sender: notes@unido.UUCP
Lines: 41
Nf-ID: #R:hoptoad:-56200:ztivax:2900005:000:1957
Nf-From: ztivax!david    Mar  6 20:46:00 1986

/* 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.
>Just by way of sanity check, our logic simulator runs at 10e-9 times
>real time (on a 15 MIPS machine). So assuming you can go 100 times
>faster with a 10 times simpler design to work on, and a 10 times faster
>simulator computer, you would run at a simulated speed of 10e-7 times
>real time. Even if you got another factor of 10, you need a lot of
>simplification to get up to real time. Lets say you can sustain 200
>MFlops on the Cray, then with a (say) 10 MHz clock on the target machine
>you only get 20 instructions per simulated cycle. That's not a lot
>of computation.

The Cray may well be useful for what they have in mind.  First of all,
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.

I am not sure if the 200MIPS taes into consideration the highly
parallel architecure of machine simulation software, so perhaps the
CRAY can do even better than that.

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.  I
believe the QM-1 was about 200KIPS, and the 8080 about 50KIPS.

The problem many QM-1 users found is that it took longer to micro-code
the emulation than to build hardware!

david smyth
free and proud of it

seismo!unido!ztivax!david