IDE: Where It All Began
The first hard drives did not have the interfaces that are common today. Instead, the drives were mounted directly onto the controller card and inserted in the ISA slot. Because of this rather impractical design, the actual controller was moved to the bottom of the hard drive without further ado, while the host adapter still had to be connected with the ISA bus.
Today this adapter is integrated directly on the motherboard, though it's really just an interface because the actual control logic is still located on the drive. Regardless of the protocol used, the length of the IDE interface has always been 16 bits. Modern motherboards offer two IDE interface channels, each of which can address two drives.
In the mid-80's, Imprimis used a proprietary interface standard for 5.25" hard drives from the Wren series (these were used and sold primarily by Compaq). When 3.5" hard drives were introduced, this standard was promptly adopted. The name of the interface and, thus, the standard was supposed to be "PC AT," but preference was given to a term that would not interfere with any trademarks: "Advanced Technology Attachment," in short, ATA, a name that is still used today.
However, not only did the name remain obscure for months, a generally accepted specification was not available either. That's why hard drives from one manufacturer often did not function with models from other sources. It was particularly problematic to detect a "slave" as a second hard drive.
At the same time, a number of different manufacturers teamed up to form the CAM committee (Common Access Method), which primarily concentrated on standardizing the SCSI specification. This organization eventually agreed to adopt the very first ATA standard based on the Imprimis interface. However, it was only in 1994, after countless changes, adaptations and amendments, that the ANSI (American National Standards Institute) accepted the proposal and declared it a standard (X3.221).
In reality, the term IDE (Integrated Drive Electronics) was coined unofficially, as there is no tangible standard behind it. Rather, it is a generic term encompassing all of the existing ATA specifications. Only Western Digital used the term "IDE" for marketing purposes, pepping it up as "Enhanced IDE."
To support drives other than hard drives (e.g., ZIP or CD-ROM drives), the ATA standard had to be expanded under the name ATAPI (ATA Packet Interface), because the ATA instruction set was never intended to support the operation of storage drives other than hard drives.