Steve's random ramblings and technical notes

Wednesday, May 18, 2005

Enable/Disable Ultra DMA in XP

Enable/disable UDMA (Ultra Direct Memory Access)
To enable/disable UDMA (Ultra Direct Memory Access) for your IDE-devices attached to the onboard controller go here :

Control Panel -> System Properties -> Device Manager -> IDE ATA/ATAPI Controllers

There select properties for your Primary- and Secondary- Channel and go to Advanced Settings where you can try to select "DMA if available" for your DVD, CDROM and HDD and use. The "PIO Only" means Programmed Input/Output where the CPU is used for data transfer which can be choppy and slow.

Note that if DMA is enabled for a device which doesn't support it then this can cause data corruption.

Note that some ATAPI devices like CD-ROM, Tape-Drive, MO-Drive is set to PIO by default, so one manually has to enable DMA as described in the beginning.

Note in WinXP if a DMA device (HDD/CD-ROM) makes more than 6 transfer timeouts then it is degraded to PIO mode (Independent of lifetime). The only way to reenable DMA is to remove the device or controller in the Device Manager (It will redetect the device automaticly).

Note Win2k/Xp without a service pack applied will only use UDMA33 on Intel onboard standard IDE-Controller. This can be upgraded to UDMA66 by adding/updating this DWORD value:

- EnableUDMA66=1
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