Magnetic tape is a medium for magnetic recording, made of a thin magnetizable coating on a long,
narrow strip of plastic film. It was developed in Germany, based on magnetic wire recording.
Devices that record and play back audio and video using magnetic tape are tape recorders
and video tape recorders. A device that stores computer data on magnetic tape is a tape drive.
Magnetic tape revolutionized broadcast and recording. When all radio was live, it allowed
programming to be recorded. At a time when gramophone records were recorded in one take,
it allowed recordings to be made in multiple parts, which were then mixed and edited with
tolerable loss in quality. It is a key technology in early computer development, allowing unparalleled
amounts of data to be mechanically created, stored for long periods, and to be rapidly
accessed. Nowadays other technologies can perform the
functions of magnetic tape. In many cases these technologies are replacing tape. Despite
this, innovation in the technology continues and companies like Sony and IBM continue to
produce new magnetic tape drives. Over years, magnetic tape can suffer from
deterioration called sticky-shed syndrome. Caused by absorption of moisture into the
binder of the tape, it can render the tape unusable.
Audio recording
Magnetic tape was invented for recording sound by Fritz Pfleumer in 1928 in Germany, based
on the invention of magnetic wire recording by Valdemar Poulsen in 1898. Pfleumer's invention
used a ferric oxide powder coating on a long strip of paper. This invention was further
developed by the German electronics company AEG, which manufactured the recording machines
and BASF, which manufactured the tape. In 1933, working for AEG, Eduard Schuller developed
the ring-shaped tape head. Previous head designs were needle-shaped and tended to shred the
tape. An important discovery made in this period was the technique of AC biasing which
improved the fidelity of the recorded audio signal by increasing the effective linearity
of the recording medium. Due to the escalating political tensions,
and the outbreak of World War II, these developments were largely kept secret. Although the Allies
knew from their monitoring of Nazi radio broadcasts that the Germans had some new form of recording
technology, the nature was not discovered until the Allies acquired captured German
recording equipment as they invaded Europe in the closing of the war. It was only after
the war that Americans, particularly Jack Mullin, John Herbert Orr, and Richard H. Ranger,
were able to bring this technology out of Germany and develop it into commercially viable
formats. A wide variety of recorders and formats have
developed since, most significantly reel-to-reel and Compact Cassette.
Video recording
The practice of recording and editing audio using magnetic tape rapidly established itself
as an obvious improvement over previous methods. Many saw the potential of making the same
improvements in recording television. Television signals are similar to audio signals. A major
difference is that video signals use more bandwidth than audio signals. Existing audio
tape recorders could not practically capture a video signal. Many set to work on resolving
this problem. Jack Mullin and the BBC both created crude working systems that involved
moving the tape across a fixed tape head at very fast speeds. Neither system saw much
use. It was the team at Ampex, led by Charles Ginsburg, that made the breakthrough of using
a spinning recording head and normal tape speeds to achieve a very high head-to-tape
speed that could record and reproduce the high bandwidth signals of video. The Ampex
system was called Quadruplex and used 2-inch-wide tape, mounted on reels like audio tape, which
wrote the signal in what is now called transverse scan.
Later improvements by other companies, particularly Sony, lead to the development of helical scan
and the enclosure of the tape reels in an easy-to-handle videocassette cartridge. Nearly
all modern videotape systems use helical scan and cartridges. Videocassette recorders used
to be common in homes and television production facilities, but many functions of the VCR
are being replaced. Since the advent of digital video and computerized video processing, optical
disc media and digital video recorders can now perform the same role as videotape. These
devices also offer improvements like random access to any scene in the recording and "live"
time shifting and have replaced videotape in many situations.
Data storage
In all tape formats, a tape drive uses motors to wind the tape from one reel to another,
passing tape heads to read, write or erase as it moves.
Magnetic tape was first used to record computer data in 1951 on the Eckert-Mauchly UNIVAC
I. The recording medium was a thin strip of one half inch wide metal, consisting of nickel-plated
bronze. Recording density was 128 characters per inch on eight tracks.
Early IBM tape drives were floor-standing drives that used vacuum columns to physically
buffer long U-shaped loops of tape. The two tape reels visibly fed tape through the columns,
intermittently spinning the reels in rapid, unsynchronized bursts, resulting in visually
striking action. Stock shots of such vacuum-column tape drives in motion were widely used to
represent "the computer" in movies and television.
Most modern magnetic tape systems use reels that are much smaller than the 10.5 inch
open reels and are fixed inside a cartridge to protect the tape and facilitate handling.
Many late 1970s and early 1980s home computers used Compact Cassettes, encoded with the Kansas
City standard, or several other "standards" such as the Tarbell Cassette Interface. Modern
cartridge formats include LTO, DLT, and DAT/DDC. Tape remains a viable alternative to disk
in some situations due to its lower cost per bit. This is a large advantage when dealing
with large amounts of data. Though the areal density of tape is lower than for disk drives,
the available surface area on a tape is far greater. The highest capacity tape media are
generally on the same order as the largest available disk drives. Tape has historically
offered enough advantage in cost over disk storage to make it a viable product, particularly
for backup, where media removability is necessary. Tape has the benefit of a comparatively long
duration during which the media can be guaranteed to retain the data stored on the media. Fifteen
to thirty years of archival data storage is cited by manufacturers of modern data tape
such as Linear Tape-Open media. In 2002, Imation received a US$11.9 million
grant from the U.S. National Institute of Standards and Technology for research into
increasing the data capacity of magnetic tape. In 2014 Sony and IBM announced that they had
been able to record 148 gigabits per square inch with magnetic tape media developed using
a new vacuum thin-film forming technology able to form extremely fine crystal particles,
allowing true tape capacity of 185 TB. See also
Magnetic tape sound recording Magnetic storage
Digital Data Storage Digital Audio Tape
References
This article is based on material taken from the Free On-line Dictionary of Computing prior
to 1 November 2008 and incorporated under the "relicensing" terms of the GFDL, version
1.3 or later. External links
History of Tape Recording Technology VidiPax Audio Format Guide