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From: hkbirke@mit-amt.MEDIA.MIT.EDU (Hal Birkeland)
Newsgroups: misc.forsale,comp.sys.mac
Subject: Re: 256K SIMMS forsale!
Summary: rated vs/ actual SIMM speed
Keywords: memory simm
Message-ID: <461@mit-amt.MEDIA.MIT.EDU>
Date: 9 Aug 89 18:18:00 GMT
References: <460@mit-amt.MEDIA.MIT.EDU> <13347@polyslo.CalPoly.EDU>
Reply-To: DarthVader@movies.media.mit.edu (Hal Birkeland)
Followup-To: comp.sys.mac
Distribution: usa
Organization: MIT Media Lab, Cambridge MA
Lines: 39

please note the followup line... IMHO, this discussion certainly does
not belong in misc.forsale anymore...

In article <13347@polyslo.CalPoly.EDU> dorourke@polyslo.CalPoly.EDU
	(David M. O'Rourke) writes: 

>adam@mit-amt.MEDIA.MIT.EDU (Adam Glass) writes: 
>>You're quite wrong. Mac II series computers will work just fine with 150ns
>>SIMM chips. For all normal use, there is no apparent slow down at all. In

[David's paragraph about Apple replacing "slow" SIMMS as a fix deleted]
>  Perhaps some hardware type on the net could explain why the 020 and 030
>in Apple's products require 120ns or better chips.
Sorry, not quite a Mac hardware type yet... 
[.signature deleted]

	Chip manufacturers are conservative. They want 100% (or some
number extermely close to this) of there chips to work at least as
well as marked. In other words, a chip rated to 12MHz will often
perform just fine at up to 16MHz (or higher if you are willing to hand
pick). Testing is expensive in large quantities, apparently far more
so than overly?-conservative speed ratings.

	100% of all SIMMs rated for 150 ns will respond in at most 150
ns with valid output. This does not imply that they will respond in
precisely 150ns, just before that. The DRAMs might be driving the
output lines 30-50ns faster than that so the manufacturer gets the
desired 100% yield.

	While not all 150ns SIMMs will work in a Mac II (I believe),
quite a few if not most might. David is right when he says that Apple
will replace the "too slow" SIMMs before anything else. Adam is right
in saying many 150ns SIMMs will work in Mac IIs.

hal@media-lab.media.mit.edu			DarthVader@movies.mit.edu
					And may the Dark Side be with you

No one would be foolish enough to claim any of my opinions, and they certainly
are not expressive of my employers...