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From: sonny@charybdis.harris-atd.com (Bob Davis)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Speed of coprocessor vs. speed of main processor
Message-ID: <3809@trantor.harris-atd.com>
Date: 11 Jun 90 20:53:24 GMT
References: <3076@crash.cts.com> <459@accucx.cc.ruu.nl> <1990Jun11.000613.6589@esegue.segue.boston.ma.us>
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Reply-To: sonny@trantor.harris-atd.com (Bob Davis)
Organization: Advanced Technology Dept., Harris Corp., Melbourne, Fl.
Lines: 22
X-Local-Date: 11 Jun 90 13:53:24 PDT

In article <1990Jun11.000613.6589@esegue.segue.boston.ma.us> johnl@esegue.segue.boston.ma.us (John R. Levine) writes:
>You can clock the 287 in two different ways.  The default is to use the same
>clock as the 286.  The 286 divides the external clock rate by 2, and the 287
>divides it by 3, so the 287 runs at an effective clock rate 2/3 of the 286.
>Alternatively, you can provide a dedicated clock for the 287, in which case
>the 287 runs at the full rate of its own clock.  There is an input on the 287
>called CKM which tells it which way it's being run.  This is all from Intel's
>286 hardware reference.
>

Does anyone know why the 287 chip designers would choose to divide
the Coprocessor clock by 3 if they did not have to? Why not run it
at the same clock rate as the CPU? 



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