Forcing Windows NT to run harddisks in DMA mode

Edit the registry:

HKLM\System\CurrentControlSet\Services\Atapi\Parameters\Device0 (Primary Device)
HKLM\System\CurrentControlSet\Services\Atapi\Parameters\Device1 (Secondary Device)

Settings of value 'DriverParameter':
0x0 OFF
0x1 AutoDetect
0x2 ON

There exists a utility DMACheck for this purpose at the Microsoft site.