Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!uunet!husc6!think!ames!sdcsvax!ucbvax!hplabs!sdcrdcf!trwrb!aero!coffee
From: coffee@aero.ARPA (Peter C. Coffee)
Newsgroups: comp.sys.intel,comp.sys.ibm.pc
Subject: Re: Clock speed on those darn 80?87 chips ...
Message-ID: <17263@aero.ARPA>
Date: Tue, 15-Sep-87 17:20:55 EDT
Article-I.D.: aero.17263
Posted: Tue Sep 15 17:20:55 1987
Date-Received: Fri, 18-Sep-87 01:21:57 EDT
References: <454@hubcap.UUCP>
Reply-To: coffee@aero.UUCP (Peter C. Coffee)
Distribution: na
Organization: The Aerospace Corporation, El Segundo, CA
Lines: 20
Keywords: 8087, 80287, et al those math processors ....
Xref: mnetor comp.sys.intel:345 comp.sys.ibm.pc:7818

In article <454@hubcap.UUCP> oolidjr@hubcap.UUCP (Joe Moll) writes:
>My dealer claims (along with a few people at our institution) that the
>coprocessor runs at (2/3) * main processor clock speed.
>
>My question is: What is the correct answer???  Seems to me that the
>clock speed is distributed out of the clock generator to both the
>coprocessor and the main processor (8086, 80286, what have you ...).

8088, 8086, and 8087 run at board clock rate.
80286 runs at 1/2 board clock rate. I don't know about the 80386.
80287 runs at 1/3 board clock rate. I don't know about the 80387.

Does this mean an 8 MHz Compaq DeskPro (8086/8087) runs intensive
floating point faster than a 10 MHz 80286 machine with the same waits?
Yes. Shrewd assembly code that really uses the numeric chip's stack,
or even reasonably well-compiled high level languages, show this ratio
in a matrix multiply benchmark that we swiped from Digital Review.
You can, in principle, feed the numeric chip its own clock rate, since
the main chip uses an FWAIT to force synchronization when needed; at
least one add-on product does precisely this.