I'm trying to troubleshoot a memory-detection problem on an old Pentium MMX system with a 430VX chipset. I've got the following memory timing options in the BIOS:

DRAM Precharge Wait State: 0, 1
DRAM Wait State: 0, 1
DRAM Read Burst (EDO/FP): x444/x444, x333/x444, x222/x333, x322/x333
DRAM Write Burst Timing: x444, x333, x222

Which options are the most conservative/have the widest compatibility?

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  • Is really a Pentium MMX system a "retro" system? – mcleod_ideafix Jul 4 '16 at 13:26
  • @mcleod_ideafix I guess that depends on your definition. It is the perfect era system for playing Windows 95 games and running certain retro OSes like OS/2 Warp and OpenNeXT. Its also contemporary to a PowerPC BeOS system or the early PowerPC Macs, would you consider those retro systems? – mnem Jul 4 '16 at 16:49
  • No, I wouldn't consider a PowerPC a retro system. Maybe in ten years or so – mcleod_ideafix Jul 4 '16 at 22:40
  • @mcleod_ideafix The Pentium MMX is 20 years old now (the first Power PC based Mac is 22). So you wouldn't have considered the Commodore 64 "retro" in 2002 (at 20 years old)? Its only been retro for the past 4 years or less, according to the metric you've laid out. Or do you consider there to be some fundamental difference other than age that determines "retro-ness"? – mnem Jul 6 '16 at 6:17
  • 1
    No significant software is being produced nowdays that can run on a C64. The last Ubuntu release can run in a Pentiun MMX based computer. I consider Pentium MMX to be obsolete, but not yet retro. 80286 could be considered retro. – mcleod_ideafix Jul 6 '16 at 6:36

You haven't told us what your SDRAM modules specifications are (PC100? PC133?). That would be useful to narrow your choices.

The most conservative settings would be:

DRAM Precharge Wait State: 1
DRAM Wait State: 1
DRAM Read Burst (EDO/FP): x444/x444
DRAM Write Burst Timing: x444

The first two insert a wait state to the processor. The remaining two uses 4 RAM clock cycles for each operation (open, read, precharge).

You may want to try also

DRAM Precharge Wait State: 1
DRAM Wait State: 1
DRAM Read Burst (EDO/FP): x322/x333
DRAM Write Burst Timing: x222

In case the problem is that the CPU is too fast for this memory: these settings will slow the CPU a bit, while operating the RAM at its top speed.

If there is some setting to modify the base clock for the processor and/or the multiply factor, use them to give your CPU a slower clock.

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