Magnetic Drum Definition/Meaning:
The earliest form of rotating magnetic storage device, used in
some of the first computers at a time when random-access store was volatile,
bulky, and expensive. The drum therefore formed the main memory of some of these
machines, the random-access stores being used only as registers. Although
random-access store developed rapidly it was still relatively expensive and the
drum was retained as a local backing store on some computers. Magnetic disk,
when introduced, took over a large part of the backing store function. Drums
remained in use however on certain systems that required faster access than was
generally provided by disk, but today they are obsolete apart from a few special
applications.
A magnetic drum consists of a cylinder whose curved surface is coated with a
suitable recording medium, either metal or iron oxide. On the head-per-track
drum the
drum rotates past a number of fixed read/ write heads, one for each track of
recorded information. On the moving-head drum the drum rotates past a single
head or small group of heads that can be moved axially to access any track. The
latter was rapidly superseded by disk stores but the head-per-track drum
survived: track selection requires only electronic switching between heads
rather than movement of the head so that such drums have much shorter access
times than disk stores.
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