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From: lm@cottage.WISC.EDU (Larry McVoy)
Newsgroups: comp.arch
Subject: Re: To RISC or to CISC .....(was V60/V70...)
Message-ID: <3604@spool.WISC.EDU>
Date: Tue, 19-May-87 20:55:52 EDT
Article-I.D.: spool.3604
Posted: Tue May 19 20:55:52 1987
Date-Received: Sat, 23-May-87 04:16:59 EDT
References: <9801@decwrl.DEC.COM> <4709@necntc.NEC.COM>
Sender: news@spool.WISC.EDU
Reply-To: lm@cottage.WISC.EDU (Larry McVoy)
Organization: U of Wisconsin CS Dept
Lines: 34

In article <4709@necntc.NEC.COM> pec@necntc.UUCP (Paul Cohen) writes:
>In Article <1204lm@cottage.WISC.EDU> writes:
>
>>So if you throw in a cache that gives you 90% hits then you've
>>just decreased memory traffic 

>In the context of the current discussion concerning microprocessor 
>architecture, a memory access should be defined as any access to the 
>memory SYSTEM and that includes any access to an off-chip cache.  I may
>be showing my ignorance, but I am not aware of any on-chip icaches that 
>get anything approaching 90% hit ratios.  In addition, in order to be 

Um, I have to admit I was thinking of the branch prediction paper when I
wrote that bit about 90% hits, but I went back and checked.  I'm still ok,
take a look at Computing Surveys, Vol. 14, No. 3, September 1982.  The paper
by AJ Smith called "Cache Memories".  In particular, pages 508-509.  I'll
grant you that he is talking about mainframe technology, but the numbers and
cache sizes are by no means out of reach of present day technology.  And all
of the figures start with miss ratios of 10%.

>> But look at what CISC is costing DEC

>Again I may be showing my ignorance, but I thought DEC's balance sheet
>was in pretty good shape these days.

Oh, yes, it's in great shape.  But tell me, would you like to buy a uVax
or a Sun3?  You say you want a uVax 'cause it says DEC and runs your code,
and besides, a Sun3 is only 2-4 times a uVaxII.  Well, ok, how about a
machine that runs 10 times faster (532, AMD 29K, etc, etc).  Dec is going
to be left in the dust if they don't trim the fat off their CPU's.  If you
really believe that I'm wrong, go buy DEC stock :-)


Larry McVoy 	        lm@cottage.wisc.edu  or  uwvax!mcvoy