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In article <17263@aero.ARPA> coffee@aero.UUCP (Peter C. Coffee) writes:

This was the question:
|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.

And this was the answer:
|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.

This isn't correct. The speed of the chip is not provided by the clock
fed to it, and there is no reason why the 80?87 can't be run at the same
speed as the 80?86, or even faster. For example, there is a company
which sells a product which plugs an 80287 runing at 10MHz into the
socket of an existing 80287. This allows an original AT (6 MHz 80286,
4MHz 80287) to run the 80287 60% faster than the main CPU. This can be
done because the 287 and 387 are run independently of the main CPU. The
8087 (as I read the manual) is run at the same speed as the CPU.

About the 80387: it can be run at 16MHz. Faster parts are promised.

What you are calling "board clock" is the speed of the crystal. Although
it is traditionally divided by 2 using an Intel clock chip or builtin
clock logic, the "speed of the chip" is rated by the output clock
signals.
-- 
	bill davidsen		(wedu@ge-crd.arpa)
  {uunet | philabs | seismo}!steinmetz!crdos1!davidsen
"Stupidity, like virtue, is its own reward" -me