Integrated Drive Electronics
IDE is a hard disk drive standard created in 1986 by Western Digital for Compaq. At the time hard disk drives (ST-506 and ESDI standards) required an external controller board. This controller board was in charge of controlling all aspects of the hard drive (sending command for moving the head unit, for example). When the communication between the controller and the hard disk drive was struck with electromagnetic interference, the controller had to resend the lost command to the hard drive, what lowered the performance of the hard drive.
Western Digital’s idea was to combine both the hard disk drive and its controller in just one piece, hence the technology name, integrated drive electronics. The hard disk drive controller was now embedded on the hard drive itself and not in an add-in board, making the hard drive faster and more reliable than ESDI and ST-506 hard drives.
Thus the connection of IDE hard drives to the PC – called ATA – is easier to be done than the existing standards at the time, ESDI and ST-506. ATA port uses a 40-pin (when using parallel communication) or a 4-pin (when using serial communication, a.k.a. SATA) connector.
In parallel ATA connection it is possible to connect two IDE drives to each port. Since each drive has its own controller, they conflict to each other, since both want to control the communication with the computer. Because of that it is necessary to disable one of the controllers, hence the names “master” for the drive that kept its controller enabled and “slave” for the drive that had its controller disabled.
This standard was quickly adopted by all other manufacturers and nowadays is the most popular hard disk drive standard.
Some years after its introduction IDE standard was revised in order to allow other types of devices such as CD-ROM, Zip drive, tape readers, etc, making it cheaper to connect these devices to the PC. Before that this kind of device had to use a proprietary interface or SCSI connection, which is expensive. This revision is called EIDE (Enhanced IDE).
Another very important innovation introduced with IDE hard drives was the kind of motor used to move the head unit. Instead of using a stepper motor like ST-506 and ESDI hard drives, which requires an individual command to move one track – for example, to move the head unit from track 0 to track 600 the controller must send 600 commands to the motor –, IDE hard drives use a motor called voice coil, which use controlling signals called servos saved on the disk’s surface. These signals are used to locate each hard disk track individually, requiring just one command to move the head unit to any track on the hard disk, no matter where it is located.
click to enlarge
Figure 1: IDE ports on a motherboard.
click to enlarge
Figure 2: "Parallel" IDE hard drive (ATA) connectors.
click to enlarge
Figure 3: "Serial" hard drive (SATA) connectors.
