Spindle Motor
1. Spindle Motor Definition
A spindle motor is a small, high-precision, high-reliability electric motor that is used to
rotate the shaft, or spindle, on which the platters are mounted in a hard disk drive (HDD).
A platter is a thin, high-precision aluminum or glass disk that is coated on both sides with
a high precision magnetic material and which is used in a HDD to store data. Modern HDDs
typically contain multiple platters, all of which are mounted on a single shaft, in order to
maximize the data storage surface in a given volume of space.
All HDD spindle motors are configured for direct driving of the platters. That is, the
rotating shaft of the motor and shaft on which the platters are mounted is a single, integral unit.
This is in contrast to most electric motors, which use gears or belts to transfer and modify their
output.
Most HDD spindle motors spin the platters at a constant rate ranging from 3,600 to 7,200
RPM. The precision of the rotational speed is maintained through the use of feedback loop
circuitry.
Among the other important characteristics of spindle motors are small size, low power
consumption, high reliability (including the ability to run for thousands of hours and tolerate
thousands of start and stop cycles without failure), minimal wobbling and vibration (due to the
tight tolerances of the platters and magnetic heads), low heat output and minimal noise output.