Path: utzoo!mnetor!uunet!steinmetz!ge-dab!codas!pdn!alan
From: alan@pdn.UUCP (Alan Lovejoy)
Newsgroups: comp.arch
Subject: Re: Harvard Architecure
Message-ID: <2626@pdn.UUCP>
Date: 25 Mar 88 14:33:09 GMT
References: <8803011911.AA06922@decwrl.dec.com> <3460011@hpsrla.HP.COM> <1071@PT.CS.CMU.EDU> <7614@apple.Apple.Com> <2594@pdn.UUCP> <373@ma.diab.UUCP>
Reply-To: alan@pdn.UUCP (0000-Alan Lovejoy)
Organization: Paradyne Corporation, Largo, Florida
Lines: 27

In article <373@ma.diab.UUCP> pf@ma.UUCP (Per Fogelstr|m) writes:
>In article <2594@pdn.UUCP> alan@pdn.UUCP (0000-Alan Lovejoy) writes:
>>The 68020 **CONSISTENTLY** benchmarks twice as fast with the instruction
>>cache turned on (compared to its being turned off).  ...............
>>
>>--alan@pdn
>
>From our experience tests has shown that turning off the internal cache in the
>"020" results in a 20% slowdown if the external memory don't have wait states.
>
>So Your figure must be from a system with slow external memory, right ??

Absolutely correct.  150ns DRAMs to be precise.  Using 45ns SRAMs, the
figure is closer to the 20% you quoted (my source gets a 30% difference with his
benchmarks and his compiler).  Somehow only the 150ns DRAM figure stuck
in my mind (perhaps because my main interest is personal computers where
45ns SRAMs are too expensive).  The numbers from the '030 also are for
relatively slow external memory and no external cache.  Sorry, but I
can't be more specific than that.

But an interesting point is raised here:  what's good for a $50,000
workstation may not be so good for a $5000 pc, and vice-versa.  What's
good for running UNIX&C may not be good for running Smalltalk, and
vice versa.  This is not new information, but the discussion in this
group tends to lose sight of it at times.

--alan@pdn