The History of Magnetic Recording
Created | Updated Dec 20, 2004
One of the foundations of human civilization 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 decedents. For thousands of years the media and methods for creating durable knowledge has evolved along with civilization itself. Stone, papyrus, paper, paint and ink worked for thousands of generations. The moveable type printing press began the mass reproduction of written information. Photography made objective recording of visual information possible.In the 18th and 19th century attention and research was made about the nature of sound and speech and 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.
Electromagnetism
In 1820 several scientists made fundamental discoveries about magnetism. Hans Oersted discovered the relationship between electricity and magnetism. Oersted 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 vis versa. In 1873 James Maxwell published "Treatise on Electricity and Magnetism" and established 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 magnetises and demagnetises 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. He was not aware of the work of Oberlin Smith. However, 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.
Poulsens 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.
Progress
Poulsens patent 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 U.S. 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 1940's.
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 1930's. 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 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.
Modern Sound
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 1950's. Development of multiple channel tape recording led to the stereo revolution in the late 1950's. Multi-track tape also revolutionized 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 1970's gave cassette recording the quality and low cost that made it the most popular recording media 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.
Video Tape
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 1940's and 1950's.
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 stationery heads and was tested in 1950. This work inspired the VERA (Vision Electronic Recording Apparatus) system developed by the BBC in the mid 1950's.
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 1950's 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 2-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 2 washing machines and could only record 1 hour 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 VTR's were a sensation and adopted by the more affluent television stations and networks. As technology for synchronization control developed in the late 1950's, videotape editing began to replace film in television production. It became faster and cheaper to use videotape to create television programs. 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 1960's Sony and Philips developed helical scan VTR's that were less expensive and even portable. The Sony CV-2000 (1964) was the first VTR marketed for consumer home use. It used ½ 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 in 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 ¾ inch tape in a cassette the size of a hardbound book. It recorded 1 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 Phillips V2000. The Phillips 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 1980's the camcorder moved from professional newsgathering to the consumer. Early camcorders utilised 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 2 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 store 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 1950's magnetic drums were used as non-volatile primary data storage and were replaced with magnetic core memory. Magnetic core memory used thousands of tiny donut shaped ferric toroids arrayed into bits and words. They were magnetised clockwise or counter 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 1970's hard disk drives used removable spindles of several platters. As data density increased the need for huge platters decreased. In 1973 IBM introduced "Winchester" technology, which placed several platters in a sealed assembly. This is still the basic design used in today's hard drives.
Another magnetic data media was invented to solve a problem caused by progress. In 1967 the IBM 370 mainframe computer was the first to use all semiconductor volatile primary memory. IBM wanted a way to load the microcode into 370's quickly and also wanted a media 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 8 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 5-¼ floppy was developed and became the mass storage basis of the early personal computers. In the early 1980's Sony developed the 3-½ 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 4 hours of 100% digital audio on a very small cassette. Phillips tried a competing system called Digital Compact Cassette (DCC) in the early 1990's 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 Future?
The primary recording competitor to magnetic tape and disks is optical recording. Since the early 1980's, 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, PDA’s and MP3 players. New technologies, such as ferro-electric (FRAM), are also coming on-line. Solid state NVRAM provides a small media 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 10-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 capacitious. They will be spinning in computers for some time to come. New digital video recorders, such as Tivo and modern 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.
Presently 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.
