Chapter 9: Hard Disks and Floppy Disks^173
The Spindle Motor
The disk platters are mounted to aspindleseparated bydisk spacersthat kee pthe platters
evenly spaced, as illustrated in Figure 9-2. The spacers provide a consistent spacing that
is needed for the read/write heads to have access to the to pof one disk and the bottom of
the one above it. In operation, the spindle rotates the platters in unison at speeds of 3,600
rpm (revolutions per minute), 4800, 5400, 7200, and—on newer devices—10,000 and
15,000 rpm. A direct-drive motor that is mounted directly below it rotates the spindle.
The motor that rotates the spindle and the disks mounted to it is called the spindle
motor. The spindle motor, shown in Figure 9-3, is always connected directly to the spindle
without using belts or gears so that the drive mechanism is free of noise and vibration,
which could, if transferred to the platters, cause data read and write problems. The spindle
motor is a vital part of the disk drive’s operation. In fact, most hard disk failures are really
spindle motor failures.
The spindle motor is a brushless and sensorless DC motor that is attached directly to
the disk spindle. There are two types of spindle motors in use:in-hub motorsthat are
placedinsidetheHDAandbottom-mountmotorsthatareattachedtothespindleoutsideofFigure 9-2. Platters are mounted on a spindle and separated by spacers