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Check and Set DMA Mode

By: Arie Slob

To view the DMA mode used by your drives, you need to open the Device Manager (Control Panel > System select the Hardware tab and press the Device Manager button) and view the properties of the IDE ATA/ATAPI controllers. Double-click on the IDE ATA/ATAPI controllers entry to expand it, the right-click on the Primary IDE Channel and Secondary IDE Channel entries (one at a time) and select Properties from the menu.


Now select the Advanced Settings tab. The Current Transfer Mode will be listed. To change, click the selection arrow on the Transfer Mode drop-down box. Remember, DMA is best, but sometimes a CD-ROM won't function properly in DMA mode. So if you find that your CD-ROM uses PIO mode, you can check to see if it will use DMA, but if you experience problems, change it back.


If you want to know which devices (hard drive or CD-ROM) are connected to a specific channel, on the View tab in Device Manager, select Devices by connection. If needed you can expand the entries by clicking on the + sign in front of the entry.


You can even see which drive partitions are on which physical hard drive (provided you have partitioned your hard drive) by right-clicking the listing for the drive you want to examine in detail, select Properties and select the Volumes tab and click the Populate button.



According to Microsoft, UDMA66 mode is disabled by default on a Windows computer with an Intel chipset that supports UDMA66. To enable UDMA66 mode you need to:

  • Make sure the device supports UDMA66 mode
  • Use a 80-pin IDE cable with the proper pin cut
  • Add a registry key

To add the registry key:

  1. Start the Registry Editor
  2. Go to HKEY_LOCAL_MACHINE \ System \ CurrentControlSet \ Control \ Class \ {4D36E96A-E325-11CE-BFC1-08002BE10318} \ 0000 \
  3. Right-click an empty space in the right pane and select New > DWORD Value
  4. Name the new value EnableUDMA66
  5. Double-click this new value, and enter 1 as it's Value data
  6. Close the registry editor
  7. Restart Windows for the changes to take effect

When you restart your computer, the UDMA66 will be enabled if it is supported by the hardware.