Right click My Computer, then properties, Hardware, Device Manager, Disk Drives, then the disk drive itself. Right click that, then Properties, then Policies. There should be a check box on Enable Write Caching.

Next, while in Device Manager, click on IDE Ata controller. Right click Primary IDE Channel, then Properties. Make sure DMA if Available is selected.

Without these two things being correct, the drive will test slower than normal. I haven't done any real world tests to see how much difference they make in normal use. Some will argue the Write Caching selection. I use that on drives that can't be disconnected, but I never choose that on a USB drive.