The Anatomy of a Hard Drive
Provided by Quantum Corporation & Data Recovery Labs, Inc.

Information storage devices are a driving force behind the digital revolution. Of these various devices, the hard drive is perhaps the most common and easily-recognized. But while many people know what a hard drive is, few really know how it is constructed or how it operates. A good way to begin building this knowledge is with a basic familiarity with the components of a desktop drive.

The "hard drive" gets its name from the part that actually stores information: a rigid disk called a platter (a), which is rotated by a spindle motor (b). To increase storage capacity, most hard drives feature two or more platters. Information is written to and read from the platter by a read/write head, located in the head stack assembly (c). An actuator arm (d) holds this assembly in place. In turn, the actuator arm is positioned by upper and lower magnets, also known as mag plates (e). The mag plates control the movement of the actuator arm across the platter surface. This movement, along with the spinning of the platter, gives the read/write head access to specific locations on the platter.

Signals that are read or written by the head are amplified by the read/write preamplifier (f) which, along with the actuator coil (g) and the associated connectors, make up the flex circuit (h). Near the flex circuit is the airlock (i). When the drive is powered down, this device locks the read/write head into the "landing zone," a safe place on the platter where no information is stored. This helps prevents data loss.
These components are encased in a base casting assembly (j) and a cover (k), which are sealed tightly in a cleanroom environment. This keeps out dust and other contaminants that can damage or destroy the drive.

Every drive also contains a printed circuit assembly (PCA) (l). The PCA houses the drive electronics that allow the hard drive to communicate with the computer, and allow all of the hard drive components to work in synch. Among these electronics are a microprocessor that controls all of the drive functions; interface electronics, which communicate with the computer's interface bus; a controller ASIC, which operates all of the controller hardware for the drive; the read channel, which encodes and decodes the data; and a motor ASIC, which drives the motor and actuator coil.

© 1997 Quantum Corporation
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Used with the permission of Quantum Corp.