HARD DISK DRIVE GUIDE
What is an IDE Hard Disk Drive?
Last updated: 2/5/2002

Integrated Drive Electronics (IDE) hard disks have been around for quite a few years.  Prior to these drives, 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.  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.

A much simpler board, commonly known as an IDE Controller, interfaced the IDE hard disk to the motherboard bus.  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.  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.  Several standards have subsequently been developed to improve upon the IDE drive and incorporate other devices, such as CD-ROMs which can operate off the IDE interfaces: Enhanced IDE (EIDE), ATAPI (ATA Packet Interface), Ultra-ATA, etc. Today, most hard disk drives manufactured for PCs are ATA/66 drives (ATA/100 is proably around the corner).  These drives use Bus Mastering and Direct Memory Access to transfer data back and forth between the disk drive and the computer memory with burst speeds up to a theoretical 66 Mega Bytes per second (MBs) without going through the processor.  Older ATA/33 (Ultra DMA) drives do the same thing at 33 MBs.  Many existing motherboards still have ATA/33 or even older IDE interfaces.  Most ATA/66 drives will work on the older IDE interfaces, but, of course, not as fast.   The other major category of disk drives use variations of the Small Computer System Interface (SCSI) and will not be covered in the first publication of this guide.

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References

3.  Technical Committee T13 AT Attachment - All the info anyone  would want on this subject in extensive detail.