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From: jpn@genrad.com (John P. Nelson)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: coprocessor... how fast???
Message-ID: <40539@genrad.UUCP>
Date: 28 Jan 91 19:46:59 GMT
References: <1991Jan27.172506.15133@ncsuvx.ncsu.edu> <1991Jan28.150353.25420@athena.mit.edu>
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Reply-To: jpn@maxwell.genrad.COM (John P. Nelson)
Organization: GenRad, Inc., Concord, Mass.
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>The general rule of thumb for 86 and 286 machines is that the coprocessor
>runs at 2/3's of the main CPU speed.

While this is (usually) true of 80286 machines, it is definitely NOT
true for 8086 or 8088 machines.  The 8087 MUST run at the same clock
rate as the main processor.  80387's and 80387SX's are generally run at
the same speed as the CPU, also.

Some 80286's use a seperate crystal to clock the 80287:  On these, the
2/3 rule doesn't work:  You really need to know the proper frequency
for the co-processor.

     john nelson

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