I doubt it's EDO, no you can't use a 72 Pin SIMM on it. Many computer specs and terms are misleading, but you can actually count the pins in the socket to know how many pins you need on the RAM chips for this. 20.

Cheers, I found these but not sure if they would sit happily with the ones installed?

https://www.ebay.co.uk/itm/251666089005

Too slow those, he says they're 150ns, but marked for 200, yeuch. They are more for 8 bits or original speed 8088s. You want 80ns or faster

BitWrangler wrote on 2023-03-08, 18:05:

Too slow those, he says they're 150ns, but marked for 200, yeuch. They are more for 8 bits or original speed 8088s. You want 80ns or faster

Can you mix and match speeds, I have found these but they are showing in the picture as 60ns? He lists them as HY534256S-70 says in description that it's just a holding picture. Will these do?

https://www.ebay.co.uk/itm/225089491227?hash= … ABk9SR6jkovzbYQ

I'll go as far as a "probably" good, in that if I had them in the parts box I'd try them. But I don't know if I'd like paying 5 quid a chip.

Too expensive. I've bought these from Aliexpress and had no issues.
https://www.aliexpress.com/item/4000417164509 … id=jJuKMsxSccLV

original_meusli wrote on 2023-03-08, 15:11:

I want to upgrade this card to 2mb but I am struggling to find what type of chips I need that are sold loose. I see the card has two banks and is only upgradable to 2mb, do I have to fill all 8 slots up with 128k EDO chips to get it to work and are they 72pin chips?

The chips you need do in fact provide 1024kilobits of storage, but not as 128k units of 8 bits (128k bytes), but as 256k units of 4 bits (256k nibbles). Thus the chips you are looking for are called "256k x 4". Cirrus cards don't need EDO chips, they need FPM chips. They are not 72-pin chips. The sockets on your card have two rows of 10 pins each, that is 20 pins in total. This chip format is called "DIP 20". Those chips are still very common on marketplaces of different reputation. You should aim for 60ns or 70ns access time (the model number should end in -7, -70, -6 or -60). Basically any 256k x 4 DIP-20 DRAM chip supports FPM, but you might want to cross-check the datasheet of a chip you are going to buy.

Thanks guys, the explanation was excellent. 😀