Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!bloom-beacon!apple!amdahl!shs
From: shs@uts.amdahl.com (Steve Schoettler)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Amiga 2500UX  Availability & Technical Stuff + Bridgeboard?
Message-ID: <0130z74c1z1010p0ANE@amdahl.uts.amdahl.com>
Date: 22 Feb 89 00:21:27 GMT
References: <839@amc.UUCP> <6030@cbmvax.UUCP>
Reply-To: shs@amdahl.uts.amdahl.com (Steve Schoettler)
Distribution: usa
Organization: Amdahl Corporation, Sunnyvale CA
Lines: 39

In article <6030@cbmvax.UUCP> daveh@cbmvax.UUCP (Dave Haynie) writes:
>in article <839@amc.UUCP>, jhall@amc.UUCP (John Hall) says:
>
>> 2.	Will there be a faster A2620 style card available?
>> 	14Mhz seems rediculous.  We are currently working on a
>> 	33Mhz 68020 emulator, probably extendable to 60Mhz!
>
>The CPU speed is the least of the issues, really.  Priced 60ns DRAM lately?
>It doesn't make sense to build a faster unit until you can give it something
>to talk to.  If enough folks are willing to pay 2x-3x what the A2620 costs
>now, maybe we can talk....

60ns RAM is not really necessary.  There are 20MHz 386 boards that
run nearly full speed with 120ns DRAM's.  This may not be a fair comparison
since I don't know how many cycles/memory reference a 386 does, but...

Suppose you could get a 90% hit rate with a fast 128K SRAM cache, then:

90% of your program would run at full processor speed, and 10% would run
at half speed, so overall the program would run at about 91% as fast as if
the machine used all fast DRAM, and the RAM cost would be much lower.

This also would cut bus traffic by a factor of about 10 (minus protocol/shared
memory overhead),  so if you want to run multiprocessors, this is the
only way to go.

Of course, you have the added development effort of designing a cache
controller and the extra cost of those chips, but cache controllers
are well understood these days, and general purpose controllers are starting
to appear on the market.

Steve -- "The cache guy"

-- 

        Steve Schoettler
        shs@uts.amdahl.com
        {sun,decwrl,pyramid,ames,uunet}!amdahl!shs
        Amdahl Corp., M/S 213, 1250 E. Arques Ave, Sunnyvale, CA 94088