Data Recovery Forums - Help & Discussions

Isabella · Joined: 15 Jun 2006 Posts: 100

What mechanism is used to position the heads over the platters? Early drives used a Stepper Motor (SM), which moved the head assembly in very small... steps.

The motor transferred it's motion to the head assembly through a metal band. The heads swung over the platters with a motion akin to an arm in it's arc. Some later drives used a worm gear to push and pull the head assembly in a straight, linear motion from the edge to the middle of the platters. These still used a Stepper Motor, and I make no distinction in TheRef(tm) between the two.

Stepper Motors were displaced by a new "stepperless" motor, which utilized Servo techniques to actually "read" where the heads were on the platters. This may seem like a mundane item to us today, but it was a revolution when it was introduced. These new motors were called "Voice Coil" or "Rotary Voice Coil" motors, because they resembled the "Voice Coils" in a speaker. The feedback for the servo-positioner was obtained by dedicating a platter surface & head, and writing positional information on that surface.

Drives that use a dedicated Servo Head will be listed that way. Manufacturers soon found that they could embed the positional information between data, and most eliminated the wasteful dedicated servo in favor of an Embedded Servo. Drives that specifically mention using this technique show an "E" in the "Servo Heads" information, though almost all drives today use it.