VOGONS


First post, by viper32cm

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I've been playing around with underclocking my Pentium 100 system and I've run into an odd problem when I run the CPU at 75Mhz. At that speed (50 Mhz FSB) my Aztech isa sound card starts dropping and holding notes. The problem goes away at the 60Mhz FSB, so it has to be related to the FSB speed I would think. However, I thought that the ISA slots ran at a fixed speed. Any ideas as to what the problem might be?

Reply 1 of 4, by Warlord

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maybe the clock divider on the system board doesn't like that bus speed, and it makes the ISA bus go too fast or too slow for some reason. between 8-10 mhz is what the isa bus should run without issues. ISA slots don't run at a fixed speed, on most systems they should run at like 8.6mhz or something by default, and on some systems you can change that.

Reply 2 of 4, by OzzFan

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The ISA bus is not necessarily fixed at one speed depending on the design of the motherboard. A lot of late 486 and Pentium era boards ran the ISA bus off a divider from the bus clock. You may have to see if your BIOS supports changing the divider to keep the ISA bus between the 8 - 10MHz range as Warlord stated.

A (mostly accurate) listing of my computer systems: http://www.shelteringoak.com/OzzNet/

Reply 3 of 4, by viper32cm

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Understood. I'll take a look for a bios option to see if I can change the divider. The computer is a late-1995 or early-1996 build, so I would hope there would be some type of accommodation for the 50Mhz FSB so the OEM could sell Pentium 75 systems using the same base components.