I think either your manual is not correct or you entered it wrong.

Closest model to that I am seeing is:
Cyrix FasMath CX-83S87-25-JP

1. What do you need a coprocessor for?
2. What brand/model of motherboard do you have?
3. Can you post pics? There are a couple different socket types for the processor to go which differs from board to board.

Maybe the model number is wrong. It should be 83S87. This is what you want. They're genuine Cyrix parts, remarked for the REVEAL brand.

https://www.ebay.com/itm/NEW-Rare-Vintage-Cyr … qYAAOSwNhpbCszA

Thanks cyclone3d and Anonymous Coward for quick replay!

Here some pictures from manual and photos:

I want to speed up the laptop, because some games are very slow

https://youtu.be/w_0MHbphfLw

This coprocessor is an FPU, it accelerates applications only if they rely on floating point instructions. No game thats running on a 25MHz 386SX will be able to make good use of it.
Sadly the 386SX is also limited to a 16bit bus so it won't be very fast no matter what upgrade you throw at it. 🙁 It's more like a very fast 286.

You can use any PLCC 387SX. I recommend the Intel one.

However, this will not speed up any game. The only game that makes use of an FPU and can run on your system is probably SimCity.

The 386SX is not any faster than a 286, there's not much you can do. Also, your laptop has a DSTN screen, which causes slow screen refresh. You won't get games running fast on it - at least not games that rely on high fps.

derSammler wrote:

The 386SX is not any faster than a 286, there's not much you can do.

You are comparing a 32-bit processor (IA32) to a 16-bit processor (286). Despite the muxed 16-bit data bus of the 386SX running 32-bit code on it makes it faster, new modes, paging unit, fast switching between real and protected mode, debugging capabilities make 286 and 386 differ like two different worlds. At least to me ).

Back in time I remember I needed FPU on my 386SX laptop as a student for Mathematica for Windows and for running PSPICE. The Q387 /Q87 emualator did its job nicely instead of a real FPU.

You may be able to upgrade to a clock doubled 486. There were a few different ones that clipped onto the old CPU. It really depends on your motherboard whether it will work or not though.

I tired one back in the day but it wouldn't work due to the motherboard being incompatible.

Good luck finding one, especially for a good price.

See here:
Upgrading a 386SX - some advice!
http://www.cpucollection.ca/TI486SXLC2-G50-WN.jpg
http://web.archive.org/web/19961104092136/htt … om/2sxinfo.html

derSammler wrote:

You can use any PLCC 387SX. I recommend the Intel one.

Why is that? The Cyrix part is better in pretty much every way...unless you consider the 387SL, which is better in that it uses less power making it more suitable for portables if you're crazy enough to lug something like this around.