Parallel ATA
Advanced Technology Attachment (ATA), is a standard interface for hard disk drives. It is also sometimes used for other devices, such as Zip Drives.
Although ATA was the only proper name for the standard all along, for marketing reasons, an early version of the standard was called Integrated Drive Electronics (IDE), and the one following it Enhanced Integrated Data Electronics (EIDE).
At a certain point, the standard was extended to working with CD-ROMs and tape drives, the extension being known as Advanced Technology Attachment Packet Interface (ATAPI), the full standard now being known as ATA/ATAPI.
In spite of this, ATA/ATAPI is still known to most end-users as IDE.
Since ATA uses chunky 40 or 80 pin ribbon cables, it has become very impractical in applications with several devices in constrained spaces such as computer cases. Sometime around 2003 there will be a transition to serial ATA (S-ATA), which uses 7-pin serial cables. The transition should be transparent to the operating system and end user since the devices and controllers will work just like they did before. Serial ATA will however add the capablity to hot swap hard drives, which was not previously possible.
When an IDE controller is sent the IDENTIFY DRIVE (0xec) command it reponds with the specifics of the hard disk it is connectd to. The operating system uses this information when booting.