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IDE/ATA Transfer Modes and Protocols
Since performance is of utmost concern when using a hard disk, the different transfer modes and protocols that a drive (and interface) supports are very important. In fact, they get more attention than any other issues and features associated with the interface! Most of the advances in newer IDE/ATA standards are oriented around creating faster ways of moving data between the hard disk and the PC system. Since the IDE/ATA interface is in essence a communication channel, support for a given transfer mode or protocol requires support from the devices on both ends of the channel. This means that both the hard disk and the system chipset and BIOS must support the mode in question.
In this section I describe all of the transfer modes and protocols used for the IDE/ATA interface. First I discuss programmed I/O (PIO) modes, the oldest IDE/ATA transfer mode. I then talk about direct memory access (DMA) modes, and then the new Ultra DMA modes that superceded regular DMA and are the transfer modes of choice for newer hardware. I also talk about a a few features and protocols related to IDE data transfer.