Hardware

Magnetic Tape

Magnetic tape is a non-volatile sequential storage medium consisting of a magnetic coating on a thin plastic strip. It is used for data collection, backup and archiving. Nearly all recording tape is of this type, whether used for video, audio storage or general purpose digital data storage using a computer.

Tape has been more economical than disks for archival data, but that is changing as disk capacities have increased enormously. If tapes are stored for the duration, they must be periodically recopied or the tightly coiled magnetic surfaces may contaminate each other.

Sequential Medium

A major drawback of tape is its sequential format. Locating a specific record requires reading every record in front of it or searching for markers that identify predefined partitions. Although most tapes are used for archiving rather than routine updating, some drives allow rewriting in place if the byte count does not change. Otherwise, updating requires copying files from the original tape to a blank tape (scratch tape) and adding the new data in between.

Uses of magnetic tape

Video recording

Video recording demands much higher bandwidth than audio recording and was made practical by the invention of helical scan. Early video recorders were reel-to-reel but modern systems use cartridge tapes and videocassette recorders are very common in homes and television production facilities, though many functions of the VCR are being replaced by optical disc media.

Data storage

The use of magnetic tape for data storage has
been one of the constants of the computer industry.

Tape has quite long data latency for random accesses since the deck must wind an average of ⅓ the tape length to move from one arbitrary data block to another. Most tape systems attempt to alleviate the intrinsic long latency, either using indexing, where a separate lookup table is maintained which gives the physical tape location for a given data block number, or by marking blocks with a tape mark that can be
detected while winding the tape at high speed.

Tape remains a viable alternative to disk due to its lower cost per bit. Tape has historically offered enough advantage in cost over disk storage to make it a viable product, particularly for backup, where media removability is also important. The rapid improvement in disk storage density and price, coupled with arguably less-vigorous innovation in tape storage, has reduced the market share of tape storage products.

Information is from http://en.wikipedia.org/wiki/Magnetic_tape
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