Like Windows 2000, Windows XP still fails to set the DMA mode correctly for the IDE device designated as the slaves on the primary IDE and secondary IDE channels. Most CD- ROMS are capable of supporting DMA mode, but the default in XP is still PIO.
Setting it to DMA won't make your CD-ROM faster, but it will consume less CPU cycles. Here's how: Open the Device Manager. One way to do that is to right click on "My Computer", select the Hardware tab, and Select Device Manager. Expand "IDE ATA/ATAPI Controllers" and double-click on "Primary IDE Channel".
Under the "Advanced Settings" tab, check the "Device 1" setting. More than likely, your current transfer mode is set to PIO. Set it to "DMA if available". Repeat the step for the "Secondary IDE Channel" if you have devices attached to it. Reboot.
"Windows XP Tips: DMA Mode for CD-ROMs"
Reference : techpraveen.com