Getting Back DMA For Your CD/DVD Drive
I'm mostly bookmarking this for my reference, but maybe somebody else will run into this on a Google search and it might help.
After struggling all week with poor DVD drive performance (DVDs were skipping really bad, data transfers were really slow, burning took forever, etc...). Come to find out that, for some reason the drive had been switched to "PIO Mode" instead of the faster DMA transfer mode. How that happened, I have no idea. I figured it happened when I upgrade the firmware for the drive last week. So switched it to use DMA if available, rebooted, and it was still in PIO mode. Removed the drive to have it reinstall/redetect on reboot, still no dice.
After looking around on Microsoft's site and reading all about the CRC errors that can cause this to happen (along with a partial fix), I came across this fix as well. Did both, and am now back up with DMA mode, and everything is hunky-dorey.