Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!purdue!tut.cis.ohio-state.edu!zaphod.mps.ohio-state.edu!van-bc!ubc-cs!alberta!calgary!news
From: news@calgary.UUCP (Network News Manager)
Newsgroups: comp.sys.mac.hardware
Subject: Re: Is OK to mix 120ns with 70ns on IIC
Summary: NO !!!
Message-ID: <2499@cs-spool.calgary.UUCP>
Date: 13 Feb 90 20:07:42 GMT
References: <656@tci.bell-atl.com> <88500005@uxh.cso.uiuc.edu>
Reply-To: sharp@ksi.cpsc.ucalgary.ca.UUCP (Maurice Sharp)
Organization: Knowledge Science Lab, U. of Calgary, Calgary, Canada.
Lines: 32

From: sharp@cpsc.ucalgary.ca (Maurice Sharp)
Path: cpsc!sharp

     Let us clear this up.  Every mac has a certain speed of memory
chip that it requires.  This speed depends on the CPU chip that the
mac is running, and perhaps some other hardware, though not usually.

     Why does it matter you may ask.  The CPU runs along at a certain
speed, and as it does so, it grabs information from memory at a
certain speed.  When memory is rated at say 80ns, it means that you
have a gaurenteed access time of 80ns for a any particular part of the
memory.  If a processor running very fast (like the IIci 68030) tried
to access slow memory (that is < 80ns), it may not get the
instruction data that it was after.  The result of this is anything
from a minor to a major heart attack for the processor.

     The bottom line, if your mac requires 80ns memory (like the
IIci), then you had better purchase at least 80ns memory.  You can
purchase faster memory (70ns...) if you want, but you should NOT
purchase slower memory.  Do so at your own peril, and that of any
applications that you are running.  I expect that the mail order
places are mearly trying to sell you what they have.

	maurice




Maurice Sharp MSc. Student
University of Calgary Computer Science Department
2500 University Drive N.W.			      sharp@ksi.cpsc.UCalgary.CA
Calgary, Alberta, T2N 1N4	                   ...!alberta!calgary!sharp