This item is from the Yet Another Enhanced IDE/Fast-ATA/ATA-2 FAQ, by John Wehman and Peter den Haan with numerous contributions by others. (v1.92).
IDE (Integrated Drive Electronics--or numerous other interpretations) and ATA (AT Attachment) are one and the same thing: a disk drive implementation designed to integrate the controller onto the drive itself, thereby reducing interface costs, and making firmware implementations easier. This low cost/easy integration created a boom in the disk drive industry, as PC integrators readily ate up the low- cost alternative. Since the late 80's, ATA (as it is properly called) has become the drive of choice for the cost inhibited buyer.