First post, by Eep386
Here's that Contaq 82C591-based ISA 486 motherboard I was talking about earlier. Board was thrashed by a VARTA battery, but I was able to restore it back to full operation after fixing some traces and replacing the two 8-bit ISA slots.
Notice the one odd QS8888-12 chip next to the cache - there are unpopulated pads for an undocumented write-back 16Kx4 SRAM TAG chip there, so I fitted some round tooled pins and fitted beforementioned chip there. The effect on performance is substantial, from 22.70MB/sec to 40.21MB/sec memory bandwidth under SPEEDSYS 4.78, using a 486DX-33 CPU.
For comparison, here's where the board initially stood on Speedsys without the dirty TAG fitted, with the 486DX-33: (ignore the HDDs in the pic, I was trying out a big pile of drives)
After fitting the 16Kx4 SRAM, things started looking a bit better:
Using an Am5x86-133 upgrade chip, an MR BIOS image I found and tuning up the cache and RAM access timings I can get it to around 52.88MB/sec. Still pretty pedestrian, but certainly much better than what it was like before.
Life isn't long enough to re-enable every hidden option in every BIOS on every board... 🙁