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From: davidsen@steinmetz.steinmetz.UUCP (William E. Davidsen Jr)
Newsgroups: comp.sys.ibm.pc,comp.arch
Subject: Re: Cache on a 286 board ?
Message-ID: <7707@steinmetz.steinmetz.UUCP>
Date: Tue, 27-Oct-87 10:40:51 EST
Article-I.D.: steinmet.7707
Posted: Tue Oct 27 10:40:51 1987
Date-Received: Fri, 30-Oct-87 03:35:51 EST
References: <2467@umn-cs.UUCP>
Reply-To: davidsen@crdos1.UUCP (bill davidsen)
Organization: General Electric CRD, Schenectady, NY
Lines: 28
Xref: mnetor comp.sys.ibm.pc:9461 comp.arch:2721

In article <2467@umn-cs.UUCP> amit@umn-cs.UUCP (Neta Amit) writes:
[ discussion of cache for 286 and 386 machines ]
|
|1. Why don't they do the same trick with 286 boards (as far as I know)?
|   Is there something more complex about the logic there or what?  

PC Designs spec sheet shows 32k of cache on their GV286. The GV386
definitely has 64k of 35/45ns memory (35ns access, 45ns cycle), I have
one. The performance boost ranges from 20-35%, depending on the program,
mode, etc. It runs at 16MHz, not 15.5, which machines run 15.5?

|2. Since most 15.5 MHz/1ws machines cannot select 12.5 MHz, are you better
|   off (for whatever reason) with a 15.5/1, or with a 12.5/0 machine?

If the performance is equal otherwise, you get a boost in F.P.
performance (assuming the 80287 runs at 2/3 CPU speed). Also, the 15.5
systems frequently run the expansion slots at half speed (7.75), while
many 12.5 machines run the bus at full speed. The fast bus helps
performance, but limits the number of boards which will work happily.

To further muddy the waters, machines like the Tandy 4000 run
interleaved memory. With 1MB the system runs 1w/s, with 2MB it runs
0w/s. Actually there may be a w/s on some accesses, but the net effect
seems to be about the same as cache.
-- 
	bill davidsen		(wedu@ge-crd.arpa)
  {uunet | philabs | seismo}!steinmetz!crdos1!davidsen
"Stupidity, like virtue, is its own reward" -me