Tweak3D has updated their Windows 2000 Hard Drive and Memory Tweak Guide. Here a snippet:

DMA, in all of its flavors, is vastly superior to the PIO data transfer method to which most computers default. For those of you who are not familiar with DMA and what is does, DMA (or UDMA) is the process in which a hard drive can transfer data directly to the system RAM with minimal involvement of the processor. When the computer is using the standard PIO mode, the processor has to direct the hard drive´s every move, which is detrimental to performance.

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