Dissecting a Quamtum 4Gb Bigfoot hard drive - pt2
by, 01-05-2012 at 05:35 PM (831 Views)
After removing the cover, we now can see the Hard Drive in its naked glory.
All modern Hard Drives are operated via a voice coil. Older hard drives used a stepper motor.
Why a voice coil instead of a stepper motor?
A stepper motor van move its spindle by small, fixed amounts. But, due to the tracks getting closer to each other, a stepper motor cannot move those small distances.
The advantage of a stepper motor is that the controlling circuitry knew exactly where the head(s) was at any given moment. But, with a voice coil, that doesn't work as the head(s) could be anywhere. What the manufacturers did, was to "format" the 4th side (for a 2-platter HDD) or the 2nd side (for a single-platter HDD) with a special layout - and the voice-coil controlling mechanism can now "read" from that special platter, and know exactly where the head(s) might be at any given moment.
Then there is another problem with stepper motors - the older variants would leave the heads on the middle of the hard drive, a prime candidate for a head crash should the HDD start up again, hence the need to "park" the heads before moving the computer. Newer stepper motor variants usually have enough power to move the entire head assembly to track 0 (closest to the spindle motor, or platter spindle) to "park" the heads.
A voice coil mechanism does the same.
One little problem, however. With a stepper motor, the heads cannot move when transporting the HDD. But, with a voice-coil, the heads can still move.
So the manufacturers got clever, and build a little cantilevered arm into the assembly, which'll stop the heads from moving when being transported. When the hard drive spins up, the air movement will cause the parking lever to move, allowing the heads to move.