From: utzoo!decvax!decwrl!sun!gnu
Newsgroups: net.micro.68k
Title: 68K vs 286 on floats
Article-I.D.: sun.201
Posted: Thu Feb 17 03:47:51 1983
Received: Mon Feb 21 20:16:10 1983
References: ima.286

Anyone who thinks the 286 (80287 co-processor really) is fast on floats
has not read the specs.  Some timings from published Intel documents:

	Load 64-bit	10 us
	Store 64-bit	21 us
	Add/Sub		14/18 us
	Mul 32-bit	19 us
	Mul 80-bit	27 us
	Div		39 us

While the chip can indeed multiply pretty fast, it takes it almost as long
to store the result in memory as it does to do the multiply!  And to load a
value, add another, and store the result takes 45 us -- our 68000 software
float is faster than that (tho: it is only operating on 32-bit floats).

I can't understand how it can take them 21 us to store 4 words in memory.

(Note, these timings are for 5MHz parts.  8MHz parts will be available
"later"...  I don't know if you can run a 5MHz 80287 with an 8MHz 80286, or
even if 8MHz 80286's are available, but of course the 8MHz is what all the
slanted comparison ads have been for.)

	John Gilmore, Sun Microsystems