After enabling and starting the automatic recognition, everything fell into place nicely, and DMA was automatically enabled by Windows.2009-11-19 – flemur13013 mentioned again in this comment that setting the disk recognition to "Auto" in the BIOS settings solved his problem of a slow, CPU-gobbling secondary hard disk.
A dramatic example was reported on 2006-12-29 by David Hähningen: If you (half asleep in the dark and with considerable force) try to put the ATA plug on the hard disk the wrong way around, the gap called "KEYPIN" (pin 20 on the plug) pushes pin 21 of the hard disk socket and bends it aside.
However, there are a few reasons why a computer may use PIO instead of DMA, particularly when it's the hard disk port that falls back, not a CD/DVD drive port.
For example, David Duberman reported in 2005 that some Dell computers have DMA disabled in their BIOS by default for the second hard disk.
For example, some newer DVDs, initially from Sony, carry a copy protection scheme that relies on defective sectors.
If you try, without using special software, to copy such a DVD (which doesn't work), then this can already trigger the problem.Occasionally a chip set or controller driver is buggy, so check with the manufacturer for updates.