🚀 go-pugleaf

In article <112400012@uxa.cso.uiuc.edu> afgg6490@uxa.cso.uiuc.edu writes:
| 
| comp.arch might be interested in a few details about the
| Cyrix math chip.  This is a 387 / Weitek compatible chip,
| boasting significant speedups.  (Biggest speedup, of course,
| is avoiding the coprocessor interface).

In article <1904@crdos1.crd.ge.COM> davidsen@crdos1.crd.ge.COM (Wm E
Davidsen Jr) asks:
>  Two questions: (1) since this is a plug-in replacement for the 80387,
>how does it avoid the coprocessor interface, and (2) in what way is it
>Weitek compatible? I haven't heard that it will run Weitek code, is this
>a typo or underpublicized feature?

(1) It is a direct 80387 replacement, using the same co-processor
interface.

(2) It is 80387 compatible, not Weitek compatible.  The prices I have
seen are intermediate between the 80387 and Weitek 3167.

The operations are greatly speeded up relative to the 80387.
Floating-point add and multiply operations finish in 6 clocks instead
of almost 40.  I don't remember the details of the 80387 coprocessor
interface, but I would guess that communication and synchronization
overhead will dominate when this chip is used.

The benchmarks published by Cyrix show speedups of typically 35% on
application code.  The bar charts are very misleading, since the range
of the abscissa is 0.8 to 1.5.  The 80387 performance is normalized to
1.0, and the Cyrix performance is around 1.3-1.4.  This makes the bars
for the Cyrix about .55 units long vs. the 0.2 unit lengths of the
bars for the 80387 --- this makes it look like the Cyrix-equipped
system is almost 3 times as fast as the 80387-equipped system....
--
John D. McCalpin - mccalpin@masig1.ocean.fsu.edu
		   mccalpin@scri1.scri.fsu.edu
		   mccalpin@delocn.udel.edu