hard disks were interfaced to a PC motherboard via an expansion board known as a hard disk controller. The drive did most of the mechanical stuff and performed basic electronic/servo functions; the controller told it in detail what to do. Hard Drive Controllers
The development of the IDE hard moved most of the electronics and firmware (low-level software on a chip) from the controller to a printed circuit board on the drive itself. In the process, a buffer/cache' memory was added to the electronics to speed-up the process of reading and writing hard disk drive data. The drive got "smarter." Overall costs went down and performance went up. IDE Hard Drives
IDE Controller A much simpler board, commonly known as an IDE Controller, interfaced the IDE hard disk to the motherboard bus.
IDE Controller? The term IDE Controller is a misnomer. It is actually nothing more than a bus interface and an interface and connector for the IDE cable going to the drive. The actual controller is on the drive. In most cases when a computer says it has a problem with the hard disk controller, it has a problem with the electronics on the drive.
Subsequently, the IDE Controller expansion board electronics and the connector for the drive cable were incorporated into most motherboards. Most of these motherboards have two IDE interfaces--a Primary and a Secondary--each of which can support two IDE devices.
IDE versus ATA The term Integrated Drive Electronics (IDE) is owned by Western Digital. Other companies, such as Maxtor, Quantum, and Seagate, use the term ATA (AT Attachment). IDE and ATA are the same thing.