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Disk Drive Control: Overview.
Bits of information are stored on and retrieved from computer disk drives
using a magnetic read/write head. This information is arranged on concentric tracks, nominally circular in shape. Positioning the read/write head over the
appropriate track is a controls problem which has a significant impact on the
performance of the drive.
Normal operation of a disk drive will require access to many different tracks.
The faster the read/write head can be moved between tracks, the faster
information can be stored or retrieved. There are economic and physical
constraints on this task. The fast transition between data tracks is usually
called "seeking."
The sensitivity of the position of the read/write head to external
disturbances is also an important consideration in the design of controllers
for disk drive servos. As computer disk drives become more mobile in laptop
or handheld applications, new bumps and vibrations become common disturbances which must not affect the positioning control of the read/write head. Maintaining the read/write head over a
particular data track is usually called "following."
The designed controller needs to address the concerns of both seeking and following for the final disk drive
performance to be both fast and reliable. Work in this lab deals with the analysis of and design of
controllers for disk drives.
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