One of the foundations of human civilisation is its ability to codify and store knowledge for subsequent generations. Art, written language and music have enabled people to pass ideas and experiences to their descendents. For thousands of years, the media and methods for creating durable knowledge have evolved along with civilisation itself. Stone, papyrus, paper, paint and ink worked for hundreds of generations. The moveable type printing press began the mass reproduction of written information. Photography made objective and subjective recording of visual information possible.
In the 18th and 19th Centuries, research was first carried out on the nature of sound and speech, and the possibility of creating mechanical devices to reproduce them. Pioneers such as De Kempelein (1791) and Leon Scott (1857) led to Thomas Edison's invention of a working phonograph (1877) that recorded sound and speech on foil or wax for playback at a later time. Other inventions of the era such as the telephone showed that electricity could be used to reproduce sound.
In 1820, several scientists made fundamental discoveries about magnetism. Hans Oersted discovered the relationship between electricity and magnetism - he demonstrated that an electrical current in a wire produced a magnetic field that could deflect a compass needle. Andre-Marie Ampere found that wires carrying electrical current exerted a magnetic force on each other. Michael Faraday began studies into the interchangeable nature of electricity and magnetism. He later demonstrates that magnetic fields can produce electrical current and vice versa. In 1873, James Maxwell published his Treatise on Electricity and Magnetism, establishing the theories of electromagnetism that are still used today.
Magnetic Recording Theory
In 1878, Oberlin Smith was inspired by a visit to the Edison laboratories in Menlo Park, New Jersey. He published a description of magnetic recording in Electrical World magazine in 1888. In this article, Smith described the basic theory of all magnetic sound recording. A string impregnated with iron filings is passed through a coil of wires. A telephone circuit converts the sound into modulated electrical currents that magnetise and demagnetise the filings as they travel past the coil. When the string is rewound and passed through the coil again, the magnetic state of the filings remodulates the current in the coil and produces an electrical signal that can reproduce the original sound. However, Smith never built his device and the theory remained untested.
Valdemar Poulsen's Telegraphone
In 1894, a Danish telephone technician named Valdemar Poulsen discovered the principles of magnetic recording. Unaware of work by Oberlin Smith, Poulsen took the principle even further by designing a hard steel wire media that could be magnetised and demagnetised continuously along its length. In 1899, he filed a patent for a steel wire magnetic 'Telegraphone' and built and demonstrated a prototype in 1900 at the Paris Exhibition. It was the first successful magnetic sound recorder. At this exhibition, Poulsen recorded the voice of Emperor Franz Joseph, which is still preserved today. It is the oldest existing magnetic recording.
Poulsen's recorder used a steel wire wrapped in grooves around a cylinder, similar in appearance to Edison's cylinder phonograph. An electromagnetic 'head' was passed over the wire for both recording and playback with a switch to change the circuit from microphone to ear speaker. Observers of the early prototypes were very pleased with the quality of the sound. It was natural and didn't have the pops, clicks and other noise of phonograph recordings. However, the sound volume level was low since no method of electrical sound amplification was available. Users had to hold a telephone like receiver to their ear and listen carefully for the playback.
Poulsen's patents were acquired by the American Telegraphone Company in 1905 and sold as dictating machines. However, the telegraphone did not compete well with wax cylinder phonographs, which were louder, more reliable and less expensive.
Two developments rekindled the practical use of magnetic recording. The first was electronic amplification using vacuum tubes. This gave magnetic recorders the sensitivity and power for loudspeaker playback. The second development was AC biasing. Carlson and Carpenter at the US Naval Research Laboratory eventually patented AC biasing in 1927. AC biasing yields more permanent recordings and lower noise with a variety of magnetic media.
Steel wire as the media for recording was further improved with the introduction of changeable reels containing the wire. The wire was wound 'reel to reel' to record and playback. Improvements and the use of wire recorders continued through the 1940s.
In 1928, Fritz Pfleumer was granted a patent in Germany for the application of magnetic powders to a strip of paper or film. Thus 'tape-recording' was born.
Substantial development and commercial competition emerged in the 1930s. Allgemeine Elektrizitatsgesellschaft (AEG) in Berlin began development of a tape-based recorder. BASF was contracted to produce magnetic tape based on Pfleumer's ideas. The tape was a cellulose acetate base with iron oxide bound to one surface. In 1935, AEG's 'Magnetophone' and BASF's tape were demonstrated at the Berlin Radio Fair. In 1936, BASF made a recording of the London Philharmonic orchestra conducted by Sir Thomas Beecham on tour in Germany. The recording was played on German radio and audiences were surprised to learn that the concert was not 'live'. The magnetophone was the first modern reel-to-reel tape recorder.
In 1937, Dr Clarence Hickman of the Bell Telephone Laboratories demonstrated new materials technology that recorded more signal on less media. This reduced the speed with which the tape had to move over the recording heads. During World War II, military use of magnetic recording - mostly stainless steel wire - further perfected the technology. Magnetic tape and wire was still mostly used for telephone and dictation recording. The recording times were too short for practical entertainment uses.
After World War II, commercial development of tape-recording took off. AEG Magnetophones captured during the war became the model for tape-based recorders by Ampex (1948), Magnecord (1948) and other American manufacturers. Magnetic recording became the standard for mastering music phonograph recordings and in radio broadcasting. Prices came down and home tape-recording began in the early 1950s. Development of multiple channel tape-recording led to the stereo revolution in the late 1950s. Multi-track tape also revolutionised music by allowing instruments and performances to be recorded individually for later mixing into a final cut. Also, small performance flaws could be easily corrected without re-recording the entire session.
In 1965, both the 8-track cartridge by Lear and the compact cassette by Philips created smaller and more convenient media for audio recording. Dolby noise reduction in the early 1970s gave cassette recording the quality and low cost that made it the most popular recording medium for the next decade. Further developments in high biasing allowed the use chromium dioxide and metal particle tape to further improve dynamic range and frequency response.
Since the first days of television, a means for rapid recording and playback of video programming was sought. In the beginning film-based 'telecine' systems were the only option. The high cost and delay to process the film greatly limited these systems. That is why most original television programming was broadcast live in the 1940s and 1950s.
As soon as sound recording was improved after World War II, research to find a method for magnetic recording of video signals was underway. The problem was the tremendous bandwidth (over 6 MHz) of a video signal compared with audio signals (about 20 KHz). Early prototype video systems attempted to use linear multitrack heads and extremely fast-moving tape. Bing Crosby helped fund one such system that had 12 tracks travelling at 100 inches/second (250 CM/s) past stationary heads and was tested in 1950. This work inspired the VERA (Vision Electronic Recording Apparatus) system developed by the BBC in the mid 1950s.
The major limitation of linear systems was the need for incredible lengths of tape to record just a few minutes of video. The VERA system used very dangerous thin steel tape on a 21" reel travelling at over 200 inches per second. The entire machine had to be enclosed in a safety cage in case the tape broke while in motion. Yet with all this complicated apparatus, the system could only record 15 minutes of monochrome 405-line video.
In America, Ampex had developed state-of-the-art audio tape recorders and in the early 1950s turned their attention to videotape. They came up with a better method. Instead of moving the tape very fast past fixed heads, they developed a fast rotating head that scanned information on a slower-moving tape. Ampex's system was called Quadruplex 2 Inch. Four heads were rotated at over 14,000 RPM and placed the recording in vertical tracks on two-inch magnetic tape. The tape only had to move at 15 inches per second, the same speed as professional audio recording, yet could record the high bandwidth of a video signal.
In 1956, Ampex introduced the first practical video tape recorder, the VRX-1000 at the National Association of Radio and Television Broadcasters convention. They cost $100,000 (over $650,000 in today's money), were the size of two washing machines and could only record one hour's worth of material on a reel of tape. Each reel of tape cost $300 ($2000 today) and could only be played back about 30 times before the oxide surface was worn off by the rotating heads. Despite the size and cost, the early Ampex VTRs were a sensation and were adopted by the more affluent television stations and networks. As technology for synchronisation control developed in the late 1950s, videotape editing began to replace film in television production. It became faster and cheaper to use videotape to create television programmes. As colour television developed, videotape followed. In 1958, RCA and its TV network NBC produced and broadcast the first prime-time colour programme completely edited and shown on videotape. It was An Evening with Fred Astaire and was a sensation that year.
In the 1960s, Sony and Philips developed helical scan VTRs that were less expensive and even portable. The Sony CV-2000 (1964) was the first VTR marketed for consumer home use. It used half-inch tape reels and only recorded in monochrome using a skip field scan method that reduced both cost and quality. However, these machines were popular for industrial and educational applications. This led to the development of cartridge/cassette systems for videotape. In 1970, Sony introduced the Umatic videocassette recorder (VCR). It used three-quarter-inch tape in a cassette the size of a hardback book. It recorded one hour of broadcast quality colour television and was an industry standard for over 20 years. Sony then introduced the Betamax home VCR and was followed by JVC's VHS format and Philips' V2000. The Philips format faded away in 1980 and eventually the Beta format also lost its market. Today, the VHS video format cassettes are the standard for analogue consumer videotape worldwide.
In the 1980s, the camcorder moved from professional newsgathering to the consumer. Early camcorders used the same Beta and VHS tape formats as home VCR decks. Camcorders shrank as quality improved. Sony's Video8 and Hi8 formats used 8mm tape in a small cassette that could record two hours of video and stereo sound. It was a very popular and high-quality analogue format.
The Computer Revolution
Since the earliest days of computers, magnetic recording has played a crucial role in digital information storage. Computers require several classes of memory. Primary memory is used to hold and execute program instructions and store temporary results. Secondary or mass storage saves results or stores other programs and data for easy retrieval. Archive or library data storage allows the backup and transfer of large quantities of data for future use. In the 1950s, magnetic drums were used as non-volatile primary data storage and were replaced with magnetic core memory. Magnetic core memory used thousands of tiny doughnut-shaped ferric toroids1 arrayed into bits and words. They were magnetised clockwise or anti-clockwise to store a 1 or a 0.
Magnetic tape for data storage began in 1951 when the UNIVAC I used steel tape running at 100 inches per second to store data. It had a data density of only 128 bits per inch of tape. Magnetic tape storage evolved into Mylar-based oxide with a data density of 6250 bits per inch. Because the tape drive operations were under computer control, tape could be used as secondary storage. Also, because the tape reels themselves were removable, data tape could also be used for archiving and backup. Like other magnetic recording, the data tape was developed into cartridges and cassettes and today several high-density tape cassette formats are in use for backup and off-line storage.
Magnetic data hard disks began in 1955 with the IBM 350 Disk File device. Unlike tape, disks can be accessed directly without fast forward or rewinding. The disk spins at a high speed and magnetic read/write heads move radially over a disk's surface to 'seek' the track containing the data needed. To increase data density, most disk drives have multiple platters with information stored on both sides. The IBM 350 used 50 platters of 24 inches in diameter. However, its capacity was only 5 MB!
Until the 1970s, hard disk drives used removable spindles of several platters. As data density increased the need for huge platters decreased. IBM introduced 'Winchester' technology in 1973, which placed several platters in a sealed assembly. This is still the basic design used in today's hard drives.
Another magnetic data medium was invented to solve a problem caused by progress. In 1967, the IBM 370 mainframe computer was the first to use all semi-conductor volatile primary memory. IBM wanted a way to load the microcode into 370s quickly and also wanted a medium that was cheap enough to mail regular software updates to its customers. By 1971, engineers came up with a thin magnetic disk enclosed in an envelope that swept dust off the surface. And thus, the floppy disk was born. It was eight inches in diameter and only held 80 KB of data, but each disk was cheap enough to support the mass distribution of software. In 1976 the 5¼ inch floppy was developed and became the mass storage basis of the early personal computers. In the early 1980s Sony developed the 3½ inch floppy and with improvements this has became the floppy standard used to the present day.
The Digital Revolution
Previous developments of magnetic storage for the computer led to digital versions of audio and videotape. The Digital Audio Tape (DAT) was introduced in 1987 by Sony and used the helical scan technology of the videocassette to record up to four hours of 100% digital audio on a very small cassette. Philips tried a competing system called Digital Compact Cassette (DCC) in the early 1990s but failed to gain much support. DAT technology is also used in computer storage as well as audio mastering.
Digital video has also been well supported by emerging magnetic tape technology. Digital video recording provides lossless copying and editing. In 1988, the D1 digital videocassette format was introduced by Sony. D1 used 19mm (3/4") tape loaded into cassettes. It was large and expensive but soon evolved into smaller and cheaper formats: D2 (1990) and D3 (Panasonic in 1991). Consumer formats such as DV (1995) and Digital8 (1997) put digital video into the home market. Digital8, DV, Mini-DV and Micro-DV, as well as the professional formats, all employ high performance magnetic tape cassettes with metal evaporative or particle tape.
The primary recording competitor to magnetic tape and disks is optical recording. Since the early 1980s, digital optical systems such as Laserdisc, CD and DVD have been replacing magnetic tape for mass-produced entertainment. Optical is easy to manufacture, more durable than tape and allows faster access to programming material. Recordable optical formats such as CD-R/RW, MiniDisc (MD) and DVD+R/RW have become very popular and support easy and cheap backup of digital information.
Solid-state non-volatile memory systems (NVRAM) are another alternative to magnetic disk and tape. CompactFlash (CF) and Secure Digital (SD) cards utilise flash RAM and are widely used in digital photography, PDAs and MP3 players. New technologies, such as ferro-electric (FRAM), are also coming online. Solid state NVRAM provides a small medium with fast access and a variety of compatible interfaces. However, current devices are limited to a few gigabits of memory and cost much more per byte than magnetic tape or disk. NVRAM technology is also limited by a finite number of read/write operations and perhaps a ten-year archive life. Until cost, capacity and durability are improved, solid-state devices will be primarily used for short-term storage and data transfers.
There will be magnetic recording of information for some time to come. Magnetic hard disks are fast, cheap and very capacious. They will be spinning in computers for the foreseeable future. Digital video recorders, such as Tivo and digital sound studios, also use the high capacity and low cost of hard disks.
Video cassettes (analogue and digital) will also be with us for a while longer. Magnetic tape is still very cost-effective and flexible. Most households use their VCR more than their DVD player. The day may come when magnetic tape cassettes are completely replaced by optical and solid state media but perhaps not. There are already several magnetic taping formats being developed for digital and High-Definition television.
At present, there are no other technologies (including optical) that have the data density of magnetic recording. Researchers continue to push magnetic recording technology and data densities of over 400 gigabits per square inch of magnetic media are being perfected. As long as the public's appetite for high fidelity, high definition and high data storage continues, magnetic recording will evolve to meet those needs.