DMA/UDMA and CD drives

by Wayne Maples [Published on 20 April 2004 / Last Updated on 20 April 2004]

None of this will work if your BIOS does not support DMA mode. You might need to check your vendors web site for new IDE controller drivers or BIOS upgrades if this does not work.

There are lots of reports about Windows 2000's DMA setting re: CD drives. Where the CD drive is in the PIO mode. DMA mode will not make CD drives run faster. What it does do is reduce the CPU load from 90% (PIO mode usage) to 10% (DMA mode usage). This gives other programs a better chance to get CPU cycles. In Windows 2000 DMA is enabled per channel, not per device: therefore if you have two devices on one IDE channel, both must be DMA capable - this is important as some CDRom drives are not DMA capable.

To check if whether the drives are in the DMA mode:

  • Right click My Computer
  • Select Manage
  • Device Manager
  • IDE ATA/ATAPI Controller
  • Primary IDE Channel
  • Advance Setting Tab
If the current transfer mode is not DMA, try Auto Detect. Reboot and check it again. If it still isn't DMA, try selecting DMA mode and then rebooting. Check the Secondary IDE Channel where one usually has CD drives connected. If they show PIO try changing them to DMA.

If your controllers and drives are DMA compatible and this doesn't work there is still hope if you have a VIA chipset and award bios. Try changing the UDMA mode in BIOS for IDE to disabled. Reboot and check to see if the drives are now in the DMA mode.

If its not Ultra DMA and your system supports UDMA, you may be able to enable it in the registry via this key:


Create a Value with the name: EnableUDMA66 of data type REG_DWORD and give it a value of 1.

Whether this is an issue in XP, I don't know. You probably should check the IDE controller mode also.

For more info:

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