Faster processor causes boot problem

Replaced a Pentium II 266MHz CPU with a secondhand Pentium II 400MHz on Supermicro P6SBA motherboard with 128MB PC100 RAM. Changed bus speed to 100MHz from 66MHz. Runs DOS programs OK, but keeps resetting when loading Windows 98. Ran DOS CPU and memory testing utilities, and both reported fault-free.

Old 266MHz processor works fine. Is there any reason why a CPU which works in DOS may not work in Windows?
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  1. Read my sig. If power isn't the problem, it's probably something wrong in BIOS settings, or by jumper. Changing from66MHz FSB to 100MHz FSB requires you to change your PCI divider from 1.2 to 1/3 and your AGP divider from 1/1 to 2/3.

    <font color=blue>At least half of all problems are caused by an insufficient power supply!</font color=blue>
  2. Quote:
    Is there any reason why a CPU which works in DOS may not work in Windows?

    If I disable the L1 cache on my P3 I can run DOS fine (386 speed!) but Windows freezes while loading. So in the BIOS make sure your caches are enabled and you may need to go a bit more conservative on memory timings or something. Windows is much more memory intensive than DOS and can easily show problems that DOS won't.

    Although I seriously doubt it, you may need to re-install Windows. The reason I doubt it is that I haven't done a clean install of Windows on my machine in over *six years*, despite changing motherboards and CPUs several times.

  3. Many thanks for your suggestions, and I'll certainly investigate these areas, though the functions of some of the BIOS parameters are beyond me, and I've really no idea where one can change the AGP and PCI divider ratios. Regarding Crashman's comments on inadequate power supplies, the PII 400 actually uses less juice than the PII 266, so I would have expected the overall load on the PSU to drop, though perhaps other components use more power on account of the higher FSB speed.

    Further to ritesh laud's mention of re-installing Windows, I did actually experiment with installing Windows 98 on a clean hard disk, using the PII 400 CPU. All went well until the point where the PC required restarting. Then, as Windows loaded, the machine rebooted itself. This cycle repeated indefinitely.
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