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View Full Version : 8087 6mhz Math Coprocessors like for IBM 5162 $10 Free S&H



luvit
May 28th, 2014, 06:14 PM
These are not mine. I picked one up for my 5162 for $10
http://www.ebay.com/itm/111053821663
EDIT: Correction on the title.. these are for 80287 Math Co-processors

Stone
May 28th, 2014, 07:31 PM
I've got an Intel D80287-10 if anybody's interested.

SpidersWeb
May 28th, 2014, 08:11 PM
Don't need a maths co-pro right now, but it's awesome you have a 5162 :thumbsup:

offensive_Jerk
May 29th, 2014, 12:13 AM
Are the Co-processor speeds supposed to match the CPU speed, or how does that work?

per
May 29th, 2014, 02:29 AM
Are the Co-processor speeds supposed to match the CPU speed, or how does that work?
As log as it match or is faster than the CPU speed it should be OK.

Stone
May 29th, 2014, 03:10 AM
Most 80286-12 processors are run with 6, 8 or 10 MhZ FPUs.

per
May 29th, 2014, 03:23 AM
Ah, I forgot! The 287 core clock can be, and often is, separate from the CPU clock. It has an on-chip clock divider that can optionally be used.

The regular AT runs the FPU core at 2/3 the speed of the CPU using the internal clock divider, while the XT286 runs it directly with a separate 4.77MHz clock.

Krille
May 29th, 2014, 03:39 AM
Most 80286-12 processors are run with 6, 8 or 10 MhZ FPUs.

287 FPU:s can run asynchronously which means they run at 2/3 of the CPU frequency. So that excludes the 6 MHz FPU unless it would actually be capable of running overclocked at 8 MHz.

I'd recommend reading "EVERYTHING YOU ALWAYS WANTED TO KNOW ABOUT MATH COPROCESSORS" (http://wiretap.area.com/Gopher/Library/Techdoc/Cpu/coproc.txt) by Norbert Juffa. It's a bit of a read but well worth the effort if you're interested in these things.

EDIT: Per was faster than me. :)

offensive_Jerk
May 29th, 2014, 04:54 AM
So would this work on a 8mhz AT then?

per
May 29th, 2014, 08:47 AM
So would this work on a 8mhz AT then?

Yes. The core NPU speed in an 8MHz AT is 5.3MHz.

cr1901
June 2nd, 2014, 05:27 PM
Good find... my 286 has been lonely and wanting a companion 287 for some time :D. I once tried using an 8087 in it before I learned that the pinouts are completely incompatible. The power supply not running the hard drive was a good hint :D!