TAKEN AT YOUR OWN RISK
XP enables DMA for Hard-Drives and CD-Roms by default on most ATA or ATAPI (IDE) devices. However, sometimes computers switch to PIO mode which is slower for data transfer - a typical reason is because of a virus. To ensure that your machine is using DMA:
1. Open 'Device Manager'
2. Double-click 'IDE ATA/ATAPI Controllers'
3. Right-click 'Primary Channel' and select 'Properties' and then 'Advanced Settings'
4. In the 'Current Transfer Mode' drop-down box, select 'DMA if Available' if the current setting is 'PIO Only'