magnetic drum
magnetic drum 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 The latter was rapidly superseded by disk stores but the head-per-track drum survived: track selection requires only electronic switching between heads rather than movement of the head so that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.
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 The latter was rapidly superseded by disk stores but the head-per-track drum survived: track selection requires only electronic switching between heads rather than movement of the head so that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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magnetic drum