Re-enabling DMA on Windows

CD-ROM and DVD-ROM drives can revert to using PIO mode, despite being set to use 'DMA if Available.' Here's how to make Windows XP redetect the DMA capabilities of the drives.

This behaviour occurs with the following conditions:

• Windows XP is the operating system
• A CD-ROM or DVD-ROM drive, which is known to support DMA mode now works only in PIO mode.
• The drive controller is set to use 'DMA if available' but reports to be only in PIO mode.

Following is the mechanism that has worked for me, please try it at your own risk, it involves hacking the registry:

1. Open RegEdit
2. Find the following KEY: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class\{4D36E96A-E325-11CE-BFC1-08002BE10318}\000x
3. The last four digits will be 0000, 0001, 0002, 0003, and so on.
4. Under each key, delete all occurences of the following values: MasterIdDataChecksum,SlaveIdDataChecksum
5. Reboot the computer. Windows will now redetect DMA settings.

Anyone who can't enable DMA mode on your hard disk controller, do the following:

To enable DMA mode using the Device Manager

1. Open Device Manager.
2. Double-click IDE ATA/ATAPI Controllers to display the list of controllers and channels.
3. Right-click the icon for the channel to which the device is connected, select Properties, and then click the Advanced Settings tab.
4. In the Current Transfer Mode drop-down box, select DMA if Available if the current setting is 'PIO Only.'

If the drop-down box already shows 'DMA if Available' but the current transfer mode is PIO, then the user must toggle the settings. That is:

• Change the selection from 'DMA if available' to PIO only, and click OK.
• Then repeat the steps above to change the selection to DMA if Available.