AST Bravo LC/MS 51xx (430TX) manual states support for only 83MHz SDRAM? \ VOGONS

AST Bravo LC/MS 51xx (430TX) manual states support for only 83MHz SDRAM?

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First post, by giantenemycat

Posted on 2026-02-07, 12:27

giantenemycat Offline

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1Any DIMMs used in this computer must meet the following specifications:
2• 168 pins, JEDEC standard
3• 83 MHz, unbuffered
4• 64 bits (non-parity only)
5• Single- or double-sided DIMMs (with certain restrictions;
6see “Memory Configurations” on page 37).
7• +3.3V

This is a bit perplexing to me. I'm not sure if this means the board is running at 83MHz FSB (and thus out of spec for a regular Socket 7), the memory can run out of sync with the FSB, or the manual is simply wrong. Anyone able to chime in and give their thoughts please?

As this is a more obscure OEM board with a fairly basic BIOS, I've not been able to verify what's actually going on with frequencies beyond the CPU core clock. I've tried Everest, CPU-Z Retro and HWinfo.

Reply 1 of 5, by Ydee

Posted on 2026-02-07, 12:49

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You can use 66MHz FSB, next step is 75 or 83MHz (ex. Cyrix?) and they need 83MHz compatible RAM - I use PC100 SDRAM in this case (not on Triton, as I dont have none)-

Reply 2 of 5, by giantenemycat

Posted on 2026-03-20, 20:49

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Ydee wrote on 2026-02-07, 12:49:

You can use 66MHz FSB, next step is 75 or 83MHz (ex. Cyrix?) and they need 83MHz compatible RAM - I use PC100 SDRAM in this case (not on Triton, as I dont have none)-

This PC only supports Pentium P54C/P55, and is intended as a stable, standard office machine. You can't adjust the FSB, and no mention of supporting Cyrix, AMD, WinChip or anything else. So I'm not sure why AST would bump the FSB to 83MHz and run the PCI out of spec.

Reply 3 of 5, by the3dfxdude

Posted on 2026-03-20, 23:07

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Unofficial, unsupported overclocking seems like the norm in those days to improve performance. AST wasn't the only ones that used the 430TX that way. I had other boards. It was almost certainly because the late Intel Pentium MMX did overclock with extra cooling. Intel competitors did also take advantage of these FSB speeds in time. Yes, that did cause the PCI go out of spec. I don't remember having trouble.

Reply 4 of 5, by giantenemycat

Posted on 2026-03-20, 23:57

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the3dfxdude wrote on 2026-03-20, 23:07:

Unofficial, unsupported overclocking seems like the norm in those days to improve performance. AST wasn't the only ones that used the 430TX that way. I had other boards. It was almost certainly because the late Intel Pentium MMX did overclock with extra cooling. Intel competitors did also take advantage of these FSB speeds in time. Yes, that did cause the PCI go out of spec. I don't remember having trouble.

I've figured it out now. Took the board out to submit to retroweb, and there is a J13 jumper I missed before that indicates only 60 and 66MHz bus speeds. The manual doesn't say anything about J13 other than to leave on pins 2-3 for all listed CPUs (P133-233MMX). Positions 1-2 and 3-4 both set to 60MHz, if I'm reading that right. So they just made a mistake saying the RAM needed to be 83MHz.

Reply 5 of 5, by the3dfxdude

Posted on 2026-03-21, 01:22

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I think it's a typo. The board was probably intended to be run at 60 or 66 MHz FSB. But usually you can also run PC100, one speed faster.

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