Since only one bank on your board can take long DIPs you only have one option for 512K cache - those fake 1024k ISST chips. They are fine when they wok, just order more of them as these counterfeits are often dead on arrival. Finding a bad one can be a tedious process. You need to remove the remaining 32k chips from the other bank. Perhaps that's why it wasn't working.

The Winbond chips won't work at 512k setting. you'd need 8 of them and you only have sockets for 4.

If you can’t maintain the same cache timing, the dual-bank 256k might be faster than single bank 512k.

douglar wrote on 2020-05-22, 18:03:

Disclaimer: I know this this is a total vanity project. It's not worth the time or money, but back in the day, I always wanted […]
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Disclaimer: I know this this is a total vanity project. It's not worth the time or money, but back in the day, I always wanted to make out the config, but it was often too expensive or too risky, because I wouldn't want to melt down by primary computer. But when I could do stuff like get 16MB of ram in the 386sx and it booted OS/2 reasonably well, it felt super cool.

Here's the 256K chips in the board today. Cache size jumper settings are silk screen on the board.
Photo May 22, 1 39 26 PM.jpg

First I got 5 of these off ebay, (4 for the cache, one for the tag) installed & jumpered, but the motherboard wouldn't post.
Photo May 22, 1 40 10 PM.jpg
Tried reinserting & rearranging. No dice. Tried using the original tag. No luck there either.
Did I just waste $7 and get the wrong type of sram? Or are they relabeled ? or maybe just total garbage??

So I then I splurged and spent $9 to get 5 of these:
Photo May 22, 1 40 21 PM.jpg
They were not a total fail. The motherboard completes the POST and reports a 512K cache, but never boots. Perhaps a bad chip?

The second order did not make sense. These are 64kx8 SRAMs, which can give you 256kB in total only. It is wrongly reporting 512kB, maybe because you did not set the jumpers correctly.
But again, it did not make any sense, when you have already 256kB cache in 2 banks, switching to 256kB in one bank is useless.

EDIT: If I am not mistaken, for single bank 512kB cache configuration a 32kx8 tag is enough.
Can you confirm that (with the manual or writings on the board)?

If yes, you have a small chance to get the 512kB cache running, because you have ordered 5 pieces of 128kx8 SRAMs, but you need only 4 then
So if there is only one bad out of this 5, then it should work.

typos corrected 😀

OK, thanks-- Why do you think they are 256kb chips? I thought the marking and number of pins suggested 512kb chips?

And yes, I agree, I think should be able to use a 256kb or 512kb tag chip in a 512KB cache, yet they included the larger socket and the vendors were selling the chips in lots of 5.

douglar wrote on 2020-05-22, 18:53:

OK, thanks-- Why do you think they are 256kb chips? I thought the marking and number of pins suggested 512kb chips?

They are 512kbit chips = 64kB. Four of them give you 256kB of cache.

Thanks for explaining that. What an unfortunate math error on my part.

You should consider, that you run the cache in single bank mode, if you apply only four chips instead of eight. In most cases you have to apply an additional wait clock in cache timings while driving cache single banked. With the result, that the system with dual banked 256kb cache runs faster than single banked 512kb cache with necessary wait cycles.
If you don’t apply the necessary wait cycles, than it leads to errors (RAM) after a heat up phase (needs some minutes). Single banked modes meaning more stress and heat to the cache chips.

It remains the advantage of more cacheable RAM with 512kb cache. Uncached RAM slows down the system significant. If you are looking for a Socket3 with 512kB cache and more, than look for a board with eight 32pin sockets. Or you should be familiar with electronics, Chipset data sheets and SMD soldering to add the missing lines to the 28pin sockets - the OPTI 895 of your board supports up to 1024kb cache.

If you can stay with 32MB RAM, you should keep the 256kb with the eight 32k8 chips.

Ebay chinese sellers are selling fakes, remarked chips (yours is one of these), and reprogrammed memory modules. I had to return twice. (S/N all same, should be unique to each module), Use AIDA64 or CPU-Z to read out the SPD for each module, don't need to do it one at a time.

For this reason, I regard chinese for fun stuff as long as it is good OEM style modules (Hynix, Micron etc) for some uses. But if I need to use it for serious use, buy from other sellers as long as it is not chinese.

I had to buy ECC memory from any sellers as long as it is not chinese.

Cheers,