My D drive which is my hard drive slave which I use for storage of my Documents and downloads and pictures, recently had been disappearing on me until I read on a geek web site how Microsoft resets your hard drive after so many errors to a PIO mode instead of the DMA mode. The solution was to go into the Device manager and to click on the IDE ATA/ATAPI controller then hit the plus sign to expand it then click on the secondary IDE controller right click on that and uninstall it then reboot. That solved my disappearing second hard drive and reset it back to the Ultra DMA Mode now all seems fine.
DMA (Direct Memory Addressing) the ability of a peripheral device, such as a disk controller, to access the memory of a computer directly, without going through the CPU. DMA makes it possible to transfer information to or from external devices much more quickly than would be possible if the CPU had to handle every byte of information during the transfer.
PIO mode
(Programmed Input/Output mode) The data transfer mode used by IDE drives. These modes use the CPU's registers for data transfer in contrast with DMA, which transfers directly between main memory and the peripheral device. For transfer rates, see IDE
Anyway these are a few of my thoughts for the day. Thanks for taking the time to read, hope you learned something I know I did while trying to define the DMA and the PIO mode.