RobDos wrote on 2021-12-22, 01:32:
I purchased 1x UM61512AK-15 64x8 and 8x IS61C1024-15N 128x8 DIP-32 SRAM modules for my PC chips M915I board, after installing the system will start to post but hangs when it switches over after detecting the hard drive, disabling cache in the BIOS will let me boot the OS.
This is the typical symptom of cache memory being bad, but not bad enough to be detected as "not present" by the POST. The cause could be the memory chips, or the board itself, like a broken address trace to the cache chips.
RobDos wrote on 2021-12-22, 01:32:
1. If I use a larger capacity chip in the slot and configure for a lower capacity, should it work? IE: only use 64K of the possible 1024K.
That depends on your board. If you configure for 64K cache, some address inputs of the cache SRAM chips are not used anymore. It will work if they are tied to a fixed level. It will fail if they are floating or still connected to host address lines. Don't count on larger chips working fine unless you reverse engineered how the cache size jumpers work.
RobDos wrote on 2021-12-22, 01:32:
2. Likely the above one answers this, but if I use a TAG ram that exceeds the capacity f the manual would it work? IE use a 64K tag ram when the configuration calls for 32K
Again, this depends on your board. Generally, if the chip is larger than the largest chip supported by your board, you don't have to be afraid of excess address bits being tied to actual address lines, but you might need to add a pull-up on the extra adress lines. Usually, using 1024 KBit chips for the tag RAM in boards that support 1M cache is no problem.
RobDos wrote on 2021-12-22, 01:32:
3. Is there anything I can do to check to see if they are fake chips
There appear to be lots of untested SRAM chips with fake ISSI labels (especially the 10ns variant that never existed in DIP package) on them. You might have gotten a batch of them. The rule of thumb is to expect a dead-on-arrival rate of 10%, so you shouldn't have more than two bad ISSI chips. Jumper your board for 512K cache (single bank), and try different sets of your 8 ISSI chips.
RobDos wrote on 2021-12-22, 01:32:
4. What speed of SRAM should I use, I've seen 10-15-20 and even 8, it's a 486DX2 intel.
Chose the slowest cache settings ("3-2-2-2") for start. That should probably even run with 25ns RAM at 33MHz FSB. If the board fails at that cache settings, something is severely broken (either the board or the chips.
