🚀 go-pugleaf

|S| Norbert Juffa (S_JUFFA@iravcl.ira.uka.de) wrote:
: In <1992Dec15.101259.6401@sei.cmu.edu> griest@ajpo.sei.cmu.edu writes:
: 
: > I have been told that you can install a 16MHz '387DX in a coprocessor
: > socket to work with a 33MHz '386DX and it will work ok (running Math
: > instructions at the 16MHz rate).  I am not convinced.  Has anyone done
: > this?  How does it work?  Are their any jumpers that must be set?
: > 
: >    Tom
: > 
:
You're probably mixing up the 287 with the 387.  The 286 coprocessor, the
287, runs asyncronously to the motherboard clock, and therefore can be
used at different speeds than the main cpu clock.  In fact, my 4 year
old 386 20Mhz motherboard has a 287 socket in it, and I'm using an Am287
12Mhz.  It works great, and is cheap as heck ;->

The 387 is syncronous, and therefore must be rated at the same speed as
the motherboard cpu i.e. you need a 387DX-33.  

It's possible, however, that Intel's 16Mhz rated coprocessors will actually
run at 33Mhz.  It's just not guaranteed and tested to that rating.  If 
you have one, just plug it in and try it out (16Mhz is yawning by todays
submicron silicon standards, so I wouldn't at all be suprised if it works).