Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!ingr!b11!lhughes
From: lhughes@b11.ingr.com (Lawrence Hughes)
Newsgroups: comp.binaries.ibm.pc.d
Subject: Re: Experience with bargain 80287
Summary: my experience with AMD 80c287
Message-ID: <8405@b11.ingr.com>
Date: 31 Jul 90 13:55:48 GMT
References: <12085@sdcc6.ucsd.edu>
Organization: Intergraph Corp. Huntsville, AL
Lines: 35

I just received my $99 AMD 80c287 chip - although they "lost" my first order,
it showed up two days after I checked back in to see what happened.... The
chip installed in my 10MHz AST Premium 286 with no problem - it operates at
2/3 the 286 clock speed, so actually this part should work ok in systems with
up to 15(?)MHz clocks (you might get by with 16MHz.. haven't tried it). I
found factor of 2 to 6 speed-ups over 286 alone, depending on how FP intensive
each APP was... well worth the $99 price...

AND NOW FOR SOMETHING COMPLETELY DIFFERENT (or at least I haven't heard anyone
mention this yet): I also have a JDR 386/25 MB that has both 387 and 287 FPP
sockets - the manual says you need a 25MHz FPP (!), but if you check with JDR,
they confirm the info in the Intel books that indicate you CAN do this if you
run the 287 socket with a lower speed clock (AIN'T no such thing as a 25MHz
287...). I tried my 10 MHz AMD 80c287 in this socket, and by golly, not only
did it work, but all timing tests showed about a 1.5 factor improvement over
the 286/287 combo... basically on FP intensive stuff, typical timings were:

	System			Time (sec)

	10 MHz 286 alone	10.0
	25 MHz 386 alone	 4.5 
	286 / 287		 3.2	(287 actually running at 6.67 MHz?)
	386 / 287		 2.4

The improvement in the 286 was greater, but the ABSOLUTE speed in the 386
was even greater - gee-- which one should I leave it in? Long term no question,
AMD is rumored to be offering a 387 deal soon... 

Also, Windows 3.0 (and everything else I tried) found the "80x87" and used it
correctly in both cases (with 286 and with 386).

BTW - anyone know how the AMD part compares with Intel, Weitek, IIT or other
287s? Some of them claim higher throughput at same clock compared to Intel...

For now, however, call 800-888-5590 for the 80c287 offer...