Path: utzoo!attcan!uunet!snorkelwacker!bloom-beacon!bu.edu!mirror!prism!rob
From: rob@prism.TMC.COM
Newsgroups: comp.sys.ibm.pc
Subject: Re: Memory cache *and* zero wait state?
Message-ID: <206900167@prism>
Date: 21 Feb 90 18:31:00 GMT
References: <20154@bcsaic.UUCP>
Lines: 26
Nf-ID: #R:bcsaic.UUCP:-2015400:prism:206900167:000:1155
Nf-From: prism.TMC.COM!rob    Feb 21 13:31:00 1990


nicholls@bcsaic.UUCP writes:

>A local vendor is selling a 25MHz '386 system with

>  1 Mb ram  '0' wait state
>  32Kb cache memory

>What's the point of having both?
>Either I'm missing something, or the presence
>of the cache should slow the system down.

  This is a little late, but there's a simple answer to this. Namely,
the main memory doesn't have 0 wait states. It's pretty common practice
these days to advertise systems as having 0 wait state memory when they 
really don't. What they usually mean is that the main memory operates
with 0 wait states some of the time (as with paged or interleaved
memory), or that the memory performance is equivalent to that of a
slower machine running at 0 wait states. Either way, it's misleading.

   Building a 386 machine that truly runs without wait states would require 
using static RAM (or very fast dynamic RAM) for main memory, and would be 
difficult to do at reasonable cost. Dell put out such a machine a few years 
ago that used static RAM throughout. It was fast, but a good caching system 
can offer nearly the same performance at far lower cost, and that's the 
route most vendors take now.