Setting the DMA Mode on IDE Drives
Sometimes Windows XP for some reason sets itself to use the PIO transfer mode on IDE channels instead of the faster DMA mode. In this case you can manually switch the IDE channel to DMA mode. This will reduce the amount of CPU cycles being used on that device.
To enable the DMA mode, access the Device Manager by right-clicking on "My Computer", then left-click on Properties. Go to the Hardware tab and click "Device Manager". Open up the branch labelled "IDE ATA/ATAPI controllers", double click on "Primary IDE Channel" and go to the Advanced Settings.
Set all of the Transfer Mode scroll boxes to "DMA if available", then click OK. Do this for each IDE controller. Notice that the value in "Current Transfer Mode" depends on your hardware and therefore can be different to the value on the screenshot.