Best guess: Same type of chips as already on there: µPD424210-60-G.

Currently, the card has 1 MiB of memory. By adding an extra 1 MiB, you "unlock" the resolutions that require more than 1 MiB. For example: 800x600x24 bpp (truecolor) or 1280x1024x256, etc.

The S3 Trio/Virge chips require Dual CAS 256K x 16 memory chips. The chips you already have provide an access time of 60ns, so the add-on chip should be at least as fast. The S3 chips still operate at 5V, so don't get low-voltage (3.3V) memory, but use standard voltage (5V) memory. The RAM chips you have are EDO chips, so it is verly likely that the Trio chip is configured to run in "single cycle EDO mode (and that's why they get away with 60 ns access time), so the upgrade should be EDO (not FPM), too.

So you need 256k x 16 EDO Dual-CAS DRAM in SOJ40 case, 5V supply voltage. The there is a common pinout used by all vendors, except for the variation Dual-CAS vs. Dual-WE, so I don't expect any problems with pinout compatibility.

Thank you very much to both - this is extremely helpful!
Now on a search, and will feed back..

Well - finding the correct chips is a problem. All 256 x 16 at 60ns in SOJ40 format seem to be FPM rather than EDO, and to be honest it seems better value to buy a second-hand card such as the S3 3D with 8MB already on board for around 8 GBP! I am not after 3D performance for games but a good 2D at higher resolution.

imkidd57 wrote on 2023-02-11, 18:43:

Well - finding the correct chips is a problem. All 256 x 16 at 60ns in SOJ40 format seem to be FPM rather than EDO, and to be honest it seems better value to buy a second-hand card such as the S3 3D with 8MB already on board for around 8 GBP! I am not after 3D performance for games but a good 2D at higher resolution.

I suggest to buy a similar graphics card (S3) which has already the full amount of 2MB.
Less stress, likely also cheaper 😉
EDIT: That means, I agree with you.

imkidd57 wrote on 2023-02-11, 18:43:

Well - finding the correct chips is a problem. All 256 x 16 at 60ns in SOJ40 format seem to be FPM rather than EDO, and to be honest it seems better value to buy a second-hand card such as the S3 3D with 8MB already on board for around 8 GBP! I am not after 3D performance for games but a good 2D at higher resolution.

Well, at 8GBP for a card with 8MB, this is no doubt the way to go.

You don't need to get chips as slow as 60ns, you could also use 35ns, 40ns, 45ns or 50ns chips. I have no affiliation with this seller, but https://www.eltradec.eu/index.php/en/w?keywor … d=78&Itemid=166 lists a lot of SOJ memory chips, and it seems the KM416C254B fits the requirements. They have more than 40 of them in stock, at 2.50€ a piece (plus shipping & handling, which I didn't look up), so you can get those modules - but this can't compete with the complete card below 10GBP.

256K x 16 bits EDO at 60ns. Any will fit the bill as long as it is EDO.

Avoid chinese sellers.

One of these: Reasonable price for 1 chip. Order two.

https://www.ebay.ca/itm/192746675929?hash=ite … ABk9SR8CCrbXIYQ

Cheers,

Many thanks again for the extra information on chip identity and possible sources. Embarassingly for me, the "S3 8MB for 8 GBP" so-called bargain was an AGP card; which I completely missed.

As am in the UK, I went for the EU option from mkarcher because overall cheaper shipping (also I remembered that site for SCSI2SD and added one of those in for a restored Powerbook 5xx).

Let's see how it goes, and many thanks again.

Okay. Should had stated where you are from. This makes big difference since some countries put VAT tax on everything.

Cheers,

Yes; apologies for that; location in profile updated.