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First post, by lowlytech

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I have an unknown 386 motherboard that currently has 64K of L2 Cache. There is a silk-screened jumper matrix on the board that shows it can go up to 256K, but am mainly interested in going to 128K, as 256K seems more inline with 486 boards in my head.

What chips do I need to go to 128K, and plus what about the TAG? Is it already sufficient or does that need to be upgraded as well. Better yet, anyone upgraded to 256K and they have 128K laying around they would be willing to sell?

Thanks again. Cache memory is still something I am horribly unfamiliar with as far as what I need.

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Reply 1 of 7, by Thermalwrong

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The current SRAM chips appear to be these ones, 8Kx8: IDT 7164 on Mouser
I think just going up to 32kx8 chips on all of them would give you the full 256KB. 128KB is probably possible too but would require knowing which 4 of the 8 sockets to populate

The TAG ram is a bit different than what I've usually seen, maybe it requires the extra two slots populated with the same chip type? You couldn't put a 32kx8 in there I think, too small.
The board silkscreen says "HM6288", which from some quick searching is a 16kx4 SRAM chip, so you will maybe need the extra two. They don't look easy to find.

It might help to post a picture of that silkscreen, it might have some clues.

Reply 2 of 7, by lowlytech

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Thanks for the reply. So it is confirmed then I need to locate or deal with the TAG before even trying to source bigger cache for 128K? I looked thru my pictures of when I had the board out and I guess I didn't take a full shot of the board. I should be able to get a picture of that cache config, I think. It is installed now in a slimline northgate case that is difficult to deal with as it is one of those you have to take the power supply out to pull out the cards so you can take the ISA header card out to take pictures. The small price for slimline convenience.

Reply 3 of 7, by lowlytech

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Additional pictures I could easily get currently..

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Reply 4 of 7, by Thermalwrong

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Hmm, I'm not sure, maybe someone else knows more?
I recall seeing mention of the TAG cache to cache size relation from a recent post, but this seems to fit your situation too: Something old and Something new (386 build)
Some of the 386 manuals I've got do state that you need the full 32kx8 TAG cache for 256KB of SRAM, but 128KB and 64KB are both okay with 8Kx8, so maybe just try fitting higher density SRAM chips into 4 of the slots

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Reply 6 of 7, by lowlytech

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Ended up getting 4 32K chips and with 4 in one bank and the other bank empty it does indeed POST with 128K cache detected. So all is well it seems. Thanks so much for the replies and suggestions.