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From: jtw@lcs.mit.edu (John Wroclawski)
Newsgroups: comp.sys.mac
Subject: Re: Nix on mixing memory speeds?
Message-ID: 
Date: 23 Sep 89 17:54:00 GMT
References: <11979@cit-vax.Caltech.Edu> <4002@phri.UUCP> <2040@leah.Albany.Edu>
	<1989Sep23.010904.7650@NCoast.ORG>
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In-reply-to: allbery@NCoast.ORG's message of 23 Sep 89 01:09:04 GMT

In article <1989Sep23.010904.7650@NCoast.ORG> allbery@NCoast.ORG (Brandon S. Allbery) writes:

   There is, by and large, only *one* case where the memory speeds would
   have to match: if the memory storage system accesses more than one
   memory chip at the same time, all of those chips must be the same
   speed or the memory access hardware will get a severe case of
   heartburn....

Jees, everybody's -so- confused.

The main memory system of the Mac is a simple clocked design with
completely fixed timing. What this means is that the SIMMs must
produce data X time after they are asked. Period. It doesn't matter if
they do it faster than that, and it doesn't matter if they do it at
different speeds, as long as the data is ready when the CPU needs it.

Perhaps this nonsense about needing the same speed for all the SIMMs
in a bank got started because the -size- of all the SIMMs in a bank
must be the same. Who knows.

John T. Wroclawski - MIT Lab for Computer Science - jtw@lcs.mit.edu