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Thunderbird and fsb

Discussion in 'AMD Thunderbird' started by Brook, Apr 7, 2004.

  1. Brook

    Brook Guest

    I've got an early socket a Athlon that uses 100 MHz front side bus. I
    read somewhere that the Thunderbird becomes unstable beyond 150MHz fsb.
    Is this true? I thought cpus didn't care much about the external memory
    speed. I think my motherboard is stuffed and would be happy to get a new
    motherboard with 200 MHz fsb and 5x multiplier. Thanks
    Brook, Apr 7, 2004
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  2. Brook

    Jim Guest

    Ok, you got all the buzz words, just not arranged correctly ;)

    The FSB is a function of the CPU, not memory or motherboard. Your older
    Athlon CPU *is* a 100MHz FSB. This FSB is then multipled by the multipler
    (works out nice, eh?) to give you the CPU speed. So if the multipler is
    say, 13, that's 13 x 100MHz = 1300MHz = 1.3GHz processor.

    Ideally, you want to keep the CPU FSB and memory freq "in sync". So a CPU
    FSB of 100MHz is best paired w/ 100MHz RAM. In this case, that would be
    PC1600 (100MHz x 2 (for DDR) x 8 (bits wide) = 1600). PC1600, hmm...,
    that's pretty old stuff! They haven't made that in a looooong time. For
    all intents and purposes, your CPU and (if you have PC1600) memory have hit
    the end of the road. I doubt you'll even find any new motherboard w/ a
    starting point of less than 133MHz for either CPU FSB or memory (PC2100).

    So dump the old stuff on eBay, shop around for a nice 200MHz motherboard,
    and have at it.


    Jim, Apr 11, 2004
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  3. Brook

    Wes Newell Guest

    I'm afraid you're mistaken. The FSB clock is generated by the MB, not the
    cpu. The cpu uses this clock to determine the speed the cpu runs at also.
    The FSB connects to the system northbridge and all data passes through it
    DDR. You are correct about the memory though, and anything else. The FSB
    connects only between the cpu and the northbridge. Anything destined for
    the cpu passes through it.
    It's only a 100Mhz FSB in the sense that is what you should run it at
    to obtain the rated speed of the cpu. You can run it anywhere you want, as
    long as the cpu multiplier doesn't try to run the cpu faster than it's
    capable of. I've run mine at anywhere from 70-215MHz.
    With DDR ram it's true you want to run in sync, but with older sdram (non
    DDR), it best to run it faster than the FSB if possible, since the FSB is
    DDR, and the ram bus isn't.
    There's really not a whole lot to gain. I can't tell the difference
    between running my cpu at 24x100 or or 12x200. Well maybe a little, but
    not as much as I would have thought. I calculated about 3% increase in
    performance for every 33MHz you go up in FSB speed, in real life apps, not
    benchmarks which can be very deceiving.
    Don't waste your time and money just changing the MB. You won't notice
    much difference. If you have to go in stages, replace the CPU first. A
    2000MHz Tbred B core or barton will do wonders for that old board. Just
    make sure it's not a newer internally multiplier locked one.
    Wes Newell, Apr 11, 2004
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