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From: davidsen@sixhub.UUCP (Wm E. Davidsen Jr)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: 287 in a 386-33 system?
Message-ID: <3289@sixhub.UUCP>
Date: 24 Feb 91 01:29:38 GMT
References: <1991Feb19.080902.21887@amd.com> <15285@uudell.dell.com>
Reply-To: davidsen@sixhub.UUCP (bill davidsen)
Organization: *IX Public Access UNIX, Schenectady NY
Lines: 27

In article <15285@uudell.dell.com> jporter@twaddle.dell.com (Jeff Porter) writes:

| I won't say that it's not possible, but I will say that it is very difficult
| to put a 80287 in a 80386-33 design.  The 287 was used in some of the early
| 386-based machines before the 387 became available, but I seriously doubt that
| there are any 33 MHz 386s with a socket for a 287.  Most 386-33s will have
| a socket for a 387 and/or Weitek coprocessor.  (The only way to get a 287
| to work in a 33 Mhz system would be to drastically slow down the clock during
| coprocessor cycles, a tricky engineering task.)

  Whoops! I agree that no one is providing a 287 socket anymore, but not
because it's hard to do. The 287 never ran at CPU speed, and always
supported async operation. This system runs a 386 at 16MHz and the 287
at 10. It was designed before the specs were available for the 387, as
were the early Compaq's. Once the 387 spec was availbale that became the
chip of choice.

  The 287 is vastly slower than the 387, but was better than no FPU at
all. The old 8087 ran with the 8086 with some strange timing
constraints (the IBM PC ran the CPU at 6MHz, and the FPU at 4MHz, as I
recall), but the 287 and later run more or less independently.

-- 
bill davidsen - davidsen@sixhub.uucp (uunet!crdgw1!sixhub!davidsen)
    sysop *IX BBS and Public Access UNIX
    moderator of comp.binaries.ibm.pc and 80386 mailing list
"Stupidity, like virtue, is its own reward" -me