Yeah you'd need a 40MHz part. I think it will say so in the manual. When the system boots, it will show an ID string at the bottom of the screen. An example of an AMI BIOS id:

51-0102-1101-00111111-101094-AMIS123-P

You can use the pause/break key to keep it on the screen to make a photo (or write it down). With that we maybe can find who made the motherboard.

This board looks a lot like yours: https://stason.org/TULARC/pc/motherboards/M/M … 486-386-AD.html

For the SIMMs, make sure they are also parity ie. they have either 3 or 9 chips, not 2 or 8. And also rated for 60ns ideally.

The naming of the front panel connectors is different but other than that it seems to be matching. 😀 Maybe a relabeled board. We'll know when we get a bios ID string.

I cut that battery off soon there is some corrosion around it. But otherwise that board looks to be in excellent shape.

Some 386 motherboards can run the FPU in async mode (slower or faster than CPU), but it it only works with intel FPUs. Your board doesn't appear to have a second oscillator socket, so it appears you'll have to get one at the same speed as the CPU. Just about any 40MHz 387 should work fine. Cyrix is supposed to be the best, but you probably wouldn't notice unless you ran specific benchmarks.

A 33Mhz FPU will most likely run just fine at 40Mhz. They are generally a bit easier / cheaper to find than the 40Mhz labeled ones though I do see some 40Mhz listed in eBay right now.

I have a PCChips M321 board with a DX40 coupled with a Cyrix Fasmath @33 MHz and it's working just fine. I don't remember what are my benchmark scores...

Thanks for all the helpful responses. I dont plan to power up again until i change/clean battery and refurb power supply. Yes i forgot about the parity stuff on simms and will try to post a pic of bios page. The hyundi ram on ebay stated 4M x 9 70ns. When looking at the chips i already have they are 60ns. No rush on it. I will wait until a 40mhz 387 fpu comes up i can afford and get that. From a screen capture the cache is 128kb but i may invest in more. Found 4 x windbond chips identical on ebay.
Thanks

cyclone3d wrote on 2020-06-23, 15:11:

A 33Mhz FPU will most likely run just fine at 40Mhz. They are generally a bit easier / cheaper to find than the 40Mhz labeled ones though I do see some 40Mhz listed in eBay right now.

Most of them probably work okay. I wouldn't want to overclock an old Cyrix 83S87 though. Around 1992 cyrix moved to the "387+" core due to troubles with the older core at 40MHz.

cyclone3d wrote on 2020-06-23, 15:11:

A 33Mhz FPU will most likely run just fine at 40Mhz. They are generally a bit easier / cheaper to find than the 40Mhz labeled ones though I do see some 40Mhz listed in eBay right now.

This is the case for me. Asus ISA-386C mobo, 386DX/40 CPU, i387DX/33 copro.

Just an update. I got the bios number. Hope this helps in identifying the motherboard.
Im just waiting for 128kb cache and 387 copro i ordered.
I gave it a complete clean and refurb the power supply too.
May i ask the coprocessors have a 68pin but my MB have a few more holes and not sure how to orientate the chip once i get it. Many thanks
Also is the 16bit opera web browser still the best to use for the system?
Many thanks

vacatedboat wrote on 2020-07-12, 22:14:

Just an update. I got the bios number. Hope this helps in identifying the motherboard. Im just waiting for 128kb cache and 387 […]
Show full quote

Just an update. I got the bios number. Hope this helps in identifying the motherboard.
Im just waiting for 128kb cache and 387 copro i ordered.
I gave it a complete clean and refurb the power supply too.
May i ask the coprocessors have a 68pin but my MB have a few more holes and not sure how to orientate the chip once i get it. Many thanks

Ok The board has marking for Cyrix 387 68 pin and Weitek W3167 which is 121 pins so your board supports both. Better to use the Cyrix or a ULSI 387. It will use just the inner two rings of pins (think of it like a 486 in a ODP socket). Pin one is labeled on the board so you should have no issue getting it installed proper, just double check before you apply power 😀
Added: a Cyrix 33Mhz 387 should work fine (since that was the fastest they made before changing name to Reveal 387).
Bad news it the BIOS string is for 1374 which WimsBios has no entry for the manufacture, iirc there was someone here with same bios string and they figured it out.

Thanks fortunately i ordered the ULSI chip.
I will do a search for a similar bios string snd have a read

vacatedboat wrote on 2020-07-13, 03:07:

Thanks fortunately i ordered the ULSI chip.
I will do a search for a similar bios string snd have a read

Great ! the ULSI 387 is a good chip ! Good luck on your search as I came up empty so far.

Added: a Cyrix 33Mhz 387 should work fine (since that was the fastest they made before changing name to Reveal 387).

Uh, Cyrix sold tonnes of 40MHz 387s under their own name. Reveal was a separate company that rebadged products from many different vendors.

The new 128kb cache memory came. Installed and changed jumper setting. It feels a bit zippy on windows. Is there a dos command where i can see how much cache i have. It no longer displays at startup. Want to make sureits 256kb.
Hope its ok to keep posting or should i make a new thread?