"Redirects drive debug commands from 0xFx to 0x2x"
I'm not sure what all the drive commands do, but I _think_ you can use them to work out what the drive is doing, for instance, after you insert a disc. Basically, sniffing the drive for info, which is how to work out how games like SMG implemented their protection. However, It's not as useful as say, DVDTool.