Magnetic Tape Definition/Meaning:
1. An information storage medium consisting of a magnetic coating
on a flexible backing in tape form. The coating usually consists of fine
particles of iron oxide suspended in an inert binder, and the backing is usually
polyester. Data is recorded by magnetic encoding of tracks on the coating
according to a particular tape formal.
Magnetic tape is wound on reels (or spools), sometimes contained within a
"cartridge or "cassette. To use magnetic tape, the reel containing the tape -
the file reel - is placed on a peripheral device known as a tape transport. (This
device is also called a magnetic tape unit (MTU), tape drive, tape deck, and
tape mechanism.) The tape transport is capable of moving the tape from the file
reel, past one or more magnetic heads, and winding it onto a take-up reel; the
latter may be associated, detachably or not. with the transport or alternatively
be contained in the cartridge or cassette.
An electrical signal is applied to the write head to record
information as a magnetic pattern on the tape; in most cases the tape passes
first over an erase head to erase any signal previously written on the tape. As
the tape passes over the read head the magnetic pattern induces an electrical
signal that can be processed electronically to recreate the signal that was
recorded. Sometimes a single read/write head is provided, with its connections
switched so that it can be used for either reading or writing; more often two
separate heads - or two gaps
and windings in the same head - are used, and this permits a read-while-write
check to be made by reading and checking information as soon as it has been
recorded (see error management).
The most common dimensions for an individual
magnetic tape - a volume - are 1/2 inch wide and 2400 feet long, wound on a 10
and 1/2 inch diameter reel; 1200 and 600 ft lengths of 1/2" tape, on 8
and 1/2" or 7" reels,
are less frequently used, and occasionally a thinner plastic backing is used to
allow 3600 ft to be wound on the standard 10 and 1/2" reel. Various other widths and
lengths of tape are used, generally in some form of cartridge.
The most important uses of magnetic tape in computer systems are as follows.
(a) Data interchange. There are international standards for the
format of data recorded on magnetic tape; it is the most widely used medium
for the interchange of data between separate computer systems, including those
of different makes, and also between systems and off-line peripherals such as
printers.
(b) Backup of magnetic disk memory, particularly fixed disks.
(c) Software distribution.
(d) Input, when the tape is written by a key-to-tape system. Tape is now rarely
used in this way.
(e) Serial processing.
Although this function was once very important, the use
of magnetic disk memories has made it obsolescent.
Magnetic tape was introduced for computer use in the 1950s, when it was already
widely used for audio and instrumentation purposes. It largely superseded
punched tape and punched cards although these remained in use for limited
applications. The demise of magnetic tape as a computer medium has often been
predicted but its use is likely to continue at least through the 1980s.
2. A term sometimes used by software and systems people to mean
magnetic tape
subsystem.
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