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From: LOGIN@amdahl.UUCP (LOGIN)
Newsgroups: net.arch
Subject: Re: Apple's new Cray
Message-ID: <2850@amdahl.UUCP>
Date: Fri, 28-Feb-86 19:20:29 EST
Article-I.D.: amdahl.2850
Posted: Fri Feb 28 19:20:29 1986
Date-Received: Sat, 1-Mar-86 23:36:30 EST
References: <90@pyramid.UUCP> <562@hoptoad.uucp>
Organization: Amdahl Corp, Sunnyvale CA
Lines: 26

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.
> 
> If it introduces one major product two months early I bet it pays for itself
> handsomely.  Or if it improves that product by 30% because they could test
> 20 or 30 options (cache? 8K cache? 64K cache? faster clock with more wait
> states?  video rams versus regular rams? ...) when their competitors have
> to guess and just try one or two.
> 
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.
-- 
Mike Taylor                        ...!{ihnp4,hplabs,amd,sun}!amdahl!mat

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