unlock frequency multiplier
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  1. #1
    Join Date
    Jun 2000
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    unlock frequency multiplier

    I have just brought a Asus P3B-F and a PIII 450 CPU. I wish to overclock it to 500MHz. How do I unlock frequency multiplier so that I can choose it to 500MHz in jumperless mode?
    Actually I had even tried it using the DIP switch in jumper mode. And set it to 500MHz but it always recognize it as 450MHz!

    How do I overclock an asus P3B-F?


  2. #2
    Join Date
    Apr 2000
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    All PIIIs are multiplier locked by Intel at the factory in order to prevent remarking. Therefore, if you wish to overclock your PIII 450MHz (4.5 * 100MHz) you would have to adjust the FSB speed instead. To acheive 500MHz with a 4.5 multiplier (locked by intel), you would have to use a FSB speed of 112MHz to get 504MHz (4.5 * 112MHz).

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  3. #3
    Join Date
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    You just discovered a dirty little Intel trick. They locked the multiplier on their CPUs several years ago. Therefore - you cannot change the multiplier. In your case it's locked at 4.5, forever.

    But you can still overclock the chip.

    Multiplier X Frontside Bus Speed = CPU core speed

    Your processor is meant to run like this:

    4.5 X 100MHz = 450MHz

    Since you can't change the '4.5' to anything higher or lower - you must raise the Frontside Bus Speed(FSB) to something higher than 100MHz in order to overclock the chip.
    You might have a 112MHz FSB setting on your motherboard. That would do this:

    4.5 X 112MHz = 504MHz

    The downside to changing the FSB speed is that the PCI and AGP(graphics) port bus speeds will be increased as well.
    The PCI bus speed is a fraction(1/3) of FSB speed. Also the AGP port speed is a fraction(2/3) of FSB.

    While most hardware can tolerate the elevated bus speeds - some can't. The data on hard drives can be corrupted if the FSB speed is raised because the IDE controller is using the PCI bus(which is running fast because the FSB has been raised).

    The FSB speed is also the speed that your RAM is operating at. So, expect memory-related errors as you approach the limit of the RAM. You can purchase memory rated for faster speeds than the PC100 you most likely have now. PC100 means the memory is good for 100MHz FSB or slower. The next available speed is PC133, good for 133MHz FSB. Your PC100 is probably good for 115MHz, sometimes more, sometimes less.

    OK, I'll stop here.

    Ask some more questions
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  4. #4
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    Jolly good show TN
    Read TN's post for the full story or mine for the summary. Both tell the same tale, one just in not so many words.

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  5. #5
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    May 2000
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    Glenville, NY, US of freakin' A
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    I suppose I'll end up reading up even more, but now from OCN, etc.

    Is there any quick way to find out if upping the FSB on certain motherboards will corrupt data on certain IDE devices?


  6. #6
    Join Date
    Feb 2000
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    Divide your FSB by 1/3 and if it is above 38Mhz then there is a chance. If you have a motherboard with a 1/4 PCI divider, then divide it by 1/4 when the 1/4 divider kicks in.
    You people who think you know everything really piss people like me off who really do know everything.
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  7. #7
    Join Date
    Jun 2000
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    2
    Thanks guys... for the info. Those people at Asus must be crazy! since the cpu is locked than y give us the setting for the Freq multiplier.

    Anyway, thanks for the HELP...

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