AGP/PCI Lock is the ability to lock the AGP and PCI bus speed, usually it's an option in the BIOS.
By default, most chipset fix the AGP and PCI bus frequency by deriviation of the FSB speed. Let's say you have a 200MHz FSB, the AGP default speed is 66MHz, so it's (200MHz/3). If you don't have AGP/PCI lock and you overclock your FSB to 250MHz. The resulting AGP speed will be 250MHz/3 = 83MHz, this is OUT of specs. and many Video Card will not handle this speed.
It's why chipset makers introduced the option to "lock" the AGP/PCI bus. In the BIOS you have an option to adjust AGP speed, you can usually choose from a list that looks like this :
- Automatic (the chipset will define the speed automatically, usually will try to keep the speed within specs. - 66MHz)
- Manual (the user can choose the speed by MHz from a wide range of speed)
- Some BIOS might give a ratio option 1/3, 1/4, 1/2, 2/3, etc... 1/3 is equivalent to 1/3 of the FSB speed.
AGP/PCI is mandatory for extreme overclocking, and today's Athlon 64 chipsets don't have this option working. So it's impossible to get the most of an Athlon 64 CPU because, usually the Video Cards or PCI cards will crash because their BUS speed are too high. nForce3 250Gb will correct this problem and have a working AGP/PCI lock.
I hope this little text helped you!
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Would you buy a potato powered chipset?