Information about Magnetic Tape

Magnetic tape is a medium for magnetic recording generally consisting of a thin magnetizable coating on a long and narrow strip of plastic. Nearly all recording tape is of this type, whether used for recording audio or video or for computer data storage. It was originally developed in Germany, based on the concept of magnetic wire recording. Devices that record and playback audio and video using magnetic tape are generally called tape recorders and video tape recorders respectively. A device that stores computer data on magnetic tape can be called a tape drive, a tape unit, or a streamer.

Magnetic tape revolutionized the broadcast and recording industries. In an age when all radio (and later television) was live, it allowed programming to be prerecorded. In a time when gramophone records were recorded in one take, it allowed recordings to be created in multiple stages and easily mixed and edited with a minimal loss in quality between generations. It is also one of the key enabling technologies in the development of modern computers. Magnetic tape allowed massive amounts of data to be stored in computers for long periods of time and rapidly accessed when needed.

As of 2007, many other technologies exist that can perform the functions of magnetic tape. In many cases these technologies are replacing tape. Despite this, innovation in the technology continues and tape is still widely used.

Audio recording

Main article: Magnetic tape sound recording

Magnetic tape was first 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 an iron 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 shredded the tape. An important discovery made in this period was the technique of AC biasing which dramatically improved the fidelity of the recorded audio signal.

Due to the international hostilities preceding World War II, these developments were largely kept secret from the rest of the world. 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.

A wide variety of recorders and formats have developed since, most significantly reel-to-reel and Compact Cassette.

Video recording

Main article: Videotape

The practice of recoding and editing audio using magnetic tape rapidly established itself as an obvious improvement over previous methods. Many people saw the potential of making the same improvements in recording television. Television ("video") signals are, in principle, very similar to audio signals. The main difference is that video signals use much more bandwidth than audio signals. This meant that the existing audio tape recorders could not capture a video signal effectively.

Many people set to work on resolving this problem. Jack Mullin (working for Bing Crosby) and the BBC both created crude working systems that involved moving the tape across a fixed tape head at very fast speeds. Neither of these systems saw much use. It was the team at Ampex, lead by Charles Ginsburg, that made the breakthrough of using a spinning recoding 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, and a 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 a easy-to-handle cartridge. Nearly all modern videotape systems use helical scan and cartridges. Videocassette recorders are very common in homes and television production facilities though 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 improvents like random access to any scene in the recording and "live" time shifting and are likely to replace videotape in many situations.

Data storage

Main article: Magnetic tape data storage

The use of magnetic tape for computer data storage has been one of the constants of the computer industry. In all formats, a tape drive (or "transport" or "deck") uses precisely-controlled motors to wind the tape from one reel to another, passing a tape head as it does.

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 (12.65 mm) wide metal, consisting of nickel-plated bronze (called Vicalloy). Recording density was 128 characters per inch (198 micrometre/character) on eight tracks.

Early IBM tape drives were mechanically sophisticated floor-standing drives that used vacuum columns to buffer long u-shaped loops of tape. When active, the two tape reels thus fed tape into or pulled tape out of the vacuum columns, intermittently spinning 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 old 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. Modern cartridge formats include LTO, DLT, and DAT/DDC.

Tape remains a viable alternative to disk due to its lower cost per bit. Though the areal density is lower than for disk drives, the available surface on a tape is far greater. The highest capacity tape media are generally on the same order as the largest available disk drives (about 1 TB in 2007.) 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.

References

This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL.

•  • [ e] Magnetic storage media
Wire (1898) • Tape (1928) • Drum (1932) • Ferrite core (1949) • Hard disk (1956) • Stripe card (1956)  MICR (1956) • Thin film (1962) • CRAM (1962)  Twistor (~1968) • Floppy disk (1969) • Bubble (~1970) • MRAM (2003)

External links

• History of Tape Recording Technology
• VidiPax Audio Format Guide