Enhanced (sometimes "Expanded") IDE is a standard electronic interface between your computer and its mass storage drives. EIDE's enhancements to Integrated Drive Electronics (IDE) make it possible to address a hard disk larger than 528 Mbytes. EIDE also provides faster access to the hard drive, support for Direct Memory Access (DMA), and support for additional drives, including CD-ROM and tape devices through the AT Attachment Packet Interface. When updating your computer with a larger hard drive (or other drives), an EIDE "controller" can be added to your computer in one of its card slot.
To access larger than 528 Mbyte drives, EIDE (or the basic input/output system that comes with it) uses a 28-bit Logical Block Address (LBA) to specify the actual cylinder, head, and sector location of data on the disk. The 28 bits of the LBA provide enough information to specify unique sectors for a device up to 8.4 GB in size.
EIDE was adopted as a standard by ANSI in 1994. ANSI calls it Advanced Technology Attachment-2 (it's also referred to as "Fast ATA").
Also see IDE.