N341256SJ-12 datasheet
View attachment 30200
Interesting. It's just a plain old 32K X 8 SRAM. No Tag function. I guess the comparators are on the PPC or built into the memory controller. It's a fast SRAM, so the 32K X 8 parts I have on hand at 55ns, wouldn't do the trick. Sigh.
Huh. I may have typed to soon. Looks like I have 457 MCM6206B in the attic. However, only the fastest speed rating would replace the N341256SJ-12. Unfortunately, I didn't note down the speed rating in my inventory. Chances of them being 12ns are pretty low.
Also, still having the same puzzlement I had in this posting:
Near the end of that post, I note that a PCI PowerMacintosh cache module that I examined contains 32K words of cache storage, but only 8K of Tag RAM. The number of address bits in both should probably match, unless the cache scheme is always storing 4 words at a time.
Happily, your Ultracache also has 4 times as many storage addresses as Tag addresses (32K vs. 128K) so at least there's consistency.
jt, I imagine the extra chip positions on the module are there so that the module could be built from lower density parts. The example Jessenator has uses two 128K chips. But they might have built the same module with eight 32K chips.
The fact that there's only room for one set and size of TAG chips suggests that the cache capacity will always be the same on this module, but the same capacity might be built out of varying numbers of different capacity chips.
