Term of the Moment
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Definition: access arm
The mechanical arm that moves the read/write head across the surface of a hard disk platter. An access arm is similar to the tone arm on a phonograph turntable. It is directed by instructions in the operating system to move the head to a specific track, and the rotation of the platter positions it over the required sector. Also called an "actuator arm" because the actuator is the motor and mechanism that moves the arm. See read/write head, sector and track.
Access Arms and Platters
The disk's access arm is a marvel of mechanical engineering as it moves at blazing speed back and forth across the surface of the platters. This large multi-platter drive is early 1990s vintage, while the tiny single-platter Microdrive next to the quarter is from the mid-2000s. See Microdrive.