IDE stands for Intelligent Drive Electronics. This is an improvement over the older
MFM style
hard drives used in the
XT-class PCs, like the original
IBM PC. The older
MFM drives had very little '
brains' in them. They only possessed the
glue logic and signal processing that moved the
heads and spun the
platters. All the intelligence was expected to be in the MFM controller card.
With the advent of the AT-style PC computer, came the AT Attachment interface (ATA), which is also confusingly called IDE. This put more and more of the drive intelligence into the drive, and less reliance into the controller. Drives became more expensive, and controllers got cheaper.
ATA/IDE, being more intelligent, were easier to work with, as well. Gone were the days of carefully specifying the exact geometry of the drives. IDE drives could report their own geometry, and even lie on your behalf to get around 1024-cylinder limits and the like. Oh, it was faster too. Just trust me that IDE is better than MFM.
IDE has come along way since the original IBM PC-AT. Enhancements to ATA-33, ATA-66 and ATA-100 make data move faster, while extensions to the ATA specs allow the bus to also control CD-ROMs, CDRs, and some tape drives.
It says much for the design that ATA is still around. SCSI is still in many ways faster, but ATA is fast enough for most, and certainly much cheaper.
The controller itself, is usually simple enough that it is often integrated in Super-IO chipsets with the serial, parallel, floppy, and other interfaces. It is almost impossible to purchase a motherboard without an IDE interface already built in. You may still find some IDE on add-on boards, but that is usually the sign of a performance-enhancing IDE card, like the Ultra-66 from Promise Technology.
IDE interfaces express themselves as a pair of 40-pin headers. Each header is connected to a cable, and each cable can be connected to 1 or two drives. When two drives are connected on a single cable, one is named the master, and the other is slave. If you only have one drive on a cable, it is either master or single, depending on the drive. You set jumpers according to the manufacturer's documentation for this. The red stripe on the cable is usually near pins one and two, and on most drives is normally supposed to be near the power connector.