DaveDoc1984 wrote on 2022-04-21, 13:58:
I have got 15ns Cache installed for the "External Cache" which I assume is L2 (the BIOS refers to this as External Cache). The chips are W24257AK-15.
So you've got 9 chips the same right? or 5? If an odd number of chips, the odd one is the tag RAM, this is the one that needs to be the fastest for everything to work right... now while they're all marked 15ns they might range in actual performance from 14.9999 to 12.0001 ns.... or might be just the wrong side of 15 if the operator was half asleep that day of testing, or someone left the side door open and it was cold, or some random event like that which over-rated a chip. Now the only place where this would cause much of a problem would be the tag RAM... so... sometimes swapping chips from one in the main banks of cache to the tag RAM (When all are same type of chips) can cure marginal cache problems... because you might have swapped a 14.9999ns performing chip for a much nicer 13.846 or something performing chip which copes much easier with the higher load/duty of being the tag RAM than the chip that was previously installed there was.
(This does work for the determined overclocker also, get the bus up to 40 or 50 and the cache is crapping, then try swapping the tag around with the other chips until you find the "best" one. In current sitch it seems it got the worst one maybe, so any of the others might be an improvement)
edit: some ppl gonna point out that 15ns should be far and away fast enough for 33mhz bus speeds, true, if it's directly connected to the bus, but 486 motherboard designers had a nasty habit of sticking a buffer or other logic of some sort in the way which introduces a several ns delay of it's own to the whole process, particularly if they didn't use the fastest available logic for this, like a 74F series, but only an LS or something. However, this little bugger if you can ID it, is likely soldered in and not so trivial to replace.
Unicorn herding operations are proceeding, but all the totes of hens teeth and barrels of rocking horse poop give them plenty of hiding spots.