Flash memory is an electronic non-volatile computer storage medium that can be electrically erased and reprogrammed. Toshiba developed flash memory from EEPROM in the early 1980s and introduced it to the market in 1984; the two main types of flash memory are named after the NOR logic gates. The individual flash memory cells exhibit internal characteristics similar to those of the corresponding gates. While EPROMs had to be erased before being rewritten, NAND-type flash memory may be written and read in blocks which are much smaller than the entire device. NOR-type flash allows a single machine word to be written – to an erased location – or read independently; the NAND type is found in memory cards, USB flash drives, solid-state drives, similar products, for general storage and transfer of data. NAND or NOR flash memory is often used to store configuration data in numerous digital products, a task made possible by EEPROM or battery-powered static RAM. One key disadvantage of flash memory is that it can only endure a small number of write cycles in a specific block.
Example applications of both types of flash memory include personal computers, PDAs, digital audio players, digital cameras, mobile phones, video games, scientific instrumentation, industrial robotics, medical electronics. In addition to being non-volatile, flash memory offers fast read access times, although not as fast as static RAM or ROM, its mechanical shock resistance helps explain its popularity over hard disks in portable devices, as does its high durability, ability to withstand high pressure and immersion in water, etc. Although flash memory is technically a type of EEPROM, the term "EEPROM" is used to refer to non-flash EEPROM, erasable in small blocks bytes; because erase cycles are slow, the large block sizes used in flash memory erasing give it a significant speed advantage over non-flash EEPROM when writing large amounts of data. As of 2013, flash memory costs much less than byte-programmable EEPROM and had become the dominant memory type wherever a system required a significant amount of non-volatile solid-state storage.
Flash memory was invented by Fujio Masuoka while working for Toshiba circa 1980. According to Toshiba, the name "flash" was suggested by Masuoka's colleague, Shōji Ariizumi, because the erasure process of the memory contents reminded him of the flash of a camera. Masuoka and colleagues presented the invention at the IEEE 1987 International Electron Devices Meeting held in San Francisco. Intel Corporation introduced the first commercial NOR type flash chip in 1988. NOR-based flash has long erase and write times, but provides full address and data buses, allowing random access to any memory location; this makes it a suitable replacement for older read-only memory chips, which are used to store program code that needs to be updated, such as a computer's BIOS or the firmware of set-top boxes. Its endurance may be from as little as 100 erase cycles for an on-chip flash memory, to a more typical 10,000 or 100,000 erase cycles, up to 1,000,000 erase cycles. NOR-based flash was the basis of early flash-based removable media.
NAND flash has reduced erase and write times, requires less chip area per cell, thus allowing greater storage density and lower cost per bit than NOR flash. However, the I/O interface of NAND flash does not provide a random-access external address bus. Rather, data must be read on a block-wise basis, with typical block sizes of hundreds to thousands of bits; this makes NAND flash unsuitable as a drop-in replacement for program ROM, since most microprocessors and microcontrollers require byte-level random access. In this regard, NAND flash is similar to other secondary data storage devices, such as hard disks and optical media, is thus suitable for use in mass-storage devices, such as memory cards; the first NAND-based removable media format was SmartMedia in 1995, many others have followed, including: MultiMediaCard Secure Digital Memory Stick, xD-Picture Card. A new generation of memory card formats, including RS-MMC, miniSD and microSD, feature small form factors. For example, the microSD card has an area of just over 1.5 cm2, with a thickness of less than 1 mm.
As of August 2017 microSD cards with capacity up to 400 GB are available. Flash memory stores information in an array of memory cells made from floating-gate transistors. In single-level cell devices, each cell stores only one bit of information. Multi-level cell devices, including triple-level cell devices, can store more than one bit per cell; the floating gate may be non-conductive. In flash memory, each memory cell resembles a standard metal-oxide-semiconductor field-effect transistor except that the transistor has two gates instead of one; the cells can be seen as an electrical switch in which current flows between two terminals and is controlled by a floating gate and a control gate. The CG is similar to the gate in other MOS transistors, but below this, there is the FG insulated all around by an oxide layer; the FG is interposed between the MOSFET channel. Because the FG is electrically isolated by its insulating layer, electrons placed on it are trapped; when the FG is charged with electrons, this charge screens the electric field from the CG, inc
History of IBM magnetic disk drives
IBM manufactured magnetic disk storage devices from 1956 to 2003, when it sold its hard disk drive business to Hitachi. Both the hard disk drive and floppy disk drive were invented by IBM and as such IBM's employees were responsible for many of the innovations in these products and their technologies; the basic mechanical arrangement of hard disk drives has not changed since the IBM 1301. Disk drive performance and characteristics are measured by the same standards now as they were in the 1950s. Few products in history have enjoyed such spectacular declines in cost and size along with dramatic improvements in capacity and performance. IBM manufactured 8-inch floppy disk drives from 1969 until the mid-1980s, but did not become a significant manufacturer of smaller-sized, 5.25- or 3.5-inch floppy disk drives. IBM always offered its magnetic disk drives for sale but did not offer them with original equipment manufacturer terms until 1981. By 1996, IBM had stopped making hard disk drives unique to its systems and was offering all its HDDs as an original equipment manufacturer.
IBM uses many terms to describe its various magnetic disk drives, such as direct access storage device, disk file and diskette file. Here, the current industry standard terms, hard disk drive and floppy disk drive, are used; the IBM 350 disk storage unit, the first disk drive, was announced by IBM as a component of the IBM 305 RAMAC computer system on September 14, 1956. A similar product, the IBM 355, was announced for the IBM 650 RAMAC computer system. RAMAC stood for "Random Access Method of Accounting and Control." The first engineering prototype 350 disk storage shipped to Zellerbach Paper Company, San Francisco, in June 1956, with production shipment beginning in November 1957 with the shipment of a unit to United Airlines in Denver, Colorado. Its design was motivated by the need for real time accounting in business; the 350 stores 5 million 6-bit characters. It has fifty 24-inch diameter disks with 100 recording surfaces; each surface has 100 tracks. The disks spin at 1200 rpm. Data transfer rate is 8,800 characters per second.
An access mechanism moves a pair of heads up and down to select a disk pair and in and out to select a recording track of a surface pair. Several improved models were added in the 1950s; the IBM RAMAC 305 system with 350 disk storage leased for $3,200 per month. The 350 was withdrawn in 1969. U. S. Patent 3,503,060 from the RAMAC program is considered to be the fundamental patent for disk drives; this first-ever disk drive was cancelled by the IBM Board of Directors because of its threat to the IBM punch card business but the IBM San Jose laboratory continued development until the project was approved by IBM's president. The 350's cabinet is 68 inches high and 29 inches wide; the RAMAC unit weighs about one ton, has to be moved around with forklifts, was transported via large cargo airplanes. According to Currie Munce, research vice president for Hitachi Global Storage Technologies, the storage capacity of the drive could have been increased beyond five million characters, but IBM's marketing department at that time was against a larger capacity drive, because they didn't know how to sell a product with more storage.
Nonetheless, double capacity versions of the 350 were announced in January 1959 and shipped the same year. In 1984, the RAMAC 350 Disk File was designated an International Historic Landmark by The American Society of Mechanical Engineers. In 2002, the Magnetic Disk Heritage Center began restoration of an IBM 350 RAMAC in collaboration with Santa Clara University. In 2005, the RAMAC restoration project relocated to the Computer History Museum in Mountain View, California and is now demonstrated to the public in the museum's Revolution exhibition; the IBM 353, used on the IBM 7030, was similar with a faster transfer rate. It has a capacity of 2,097,152 64-bit words or 134,217,728 bits and transferred 125,000 words per second. A prototype unit shipped in late 1960 was the first disk drive to use one head per surface flying on a layer of compressed air as in the older head design of the IBM 350 disk storage. Production 353s used self-flying heads the same as those of the 1301; the IBM 355 was announced on September 14, 1956 as an addition to the popular IBM 650.
It stored 6 million decimal digits. Data was transferred to and from the IBM 653 magnetic core memory, an IBM 650 option that stored just sixty 10-digit words, enough for a single sector of disk or tape data; the IBM 1405 Disk Storage Unit was announced in 1961 and was designed for use with the IBM 1400 series, medium scale business computers. The 1405 Model 1 has a storage capacity of 10 million alphanumeric characters on 25 disks. Model 2 has a storage capacity of 20 million alphanumeric characters on 50 disks. In both models the disks were stacked vertically on a shaft rotating at 1200 rpm; each side of each disk has 200 tracks divided into 5 sectors. Sectors 0-4 were on the top surface and 5-9 were on the bottom surface; each sector held either 200 characters. One to three forked-shaped access arms each contained two read-write heads, one for the top of the disk and the other for the bottom of the same disk; the access arms were mounted on a carriage alongside the disk array. During a seek operation an access arm moved, under electronic control, vertically to seek a disk 00-49 and horizontally to seek a track 00-199.
A disk array is a disk storage system which contains multiple disk drives. It is differentiated from a disk enclosure, in that an array has cache memory and advanced functionality, like RAID and virtualization. Components of a typical disk array include: Disk array controllers Cache in form of both volatile random-access memory and non-volatile flash memory. Disk enclosures for electronic solid-state drives. Power suppliesTypically a disk array provides increased availability and maintainability by using additional redundant components up to the point where all single points of failure are eliminated from the design. Additionally, disk array components are hot-swappable. Disk arrays are divided into categories: Network attached storage arrays Storage area network arrays: Modular SAN arrays Monolithic SAN arrays Utility Storage Arrays Storage virtualizationPrimary vendors of storage systems include Coraid, Inc. DataDirect Networks, Dell EMC, Hewlett Packard Enterprise, Hitachi Data Systems, Huawei, IBM, NetApp, Oracle Corporation, Pure Storage and other companies that act as OEM for the above vendors and do not themselves market the storage components they manufacture
A punched card or punch card is a piece of stiff paper that can be used to contain digital data represented by the presence or absence of holes in predefined positions. Digital data can be used for data processing applications or, in earlier examples, used to directly control automated machinery. Punched cards were used through much of the 20th century in the data processing industry, where specialized and complex unit record machines, organized into semiautomatic data processing systems, used punched cards for data input and storage. Many early digital computers used punched cards prepared using keypunch machines, as the primary medium for input of both computer programs and data. While punched cards are now obsolete as a storage medium, as of 2012, some voting machines still use punched cards to record votes. Basile Bouchon developed the control of a loom by punched holes in paper tape in 1725; the design was improved by his assistant Jean-Baptiste Falcon and Jacques Vaucanson Although these improvements controlled the patterns woven, they still required an assistant to operate the mechanism.
In 1804 Joseph Marie Jacquard demonstrated a mechanism to automate loom operation. A number of punched cards were linked into a chain of any length; each card held the instructions for selecting the shuttle for a single pass. It is considered an important step in the history of computing hardware. Semyon Korsakov was reputedly the first to propose punched cards in informatics for information store and search. Korsakov announced his new method and machines in September 1832. Charles Babbage proposed the use of "Number Cards", "pierced with certain holes and stand opposite levers connected with a set of figure wheels... advanced they push in those levers opposite to which there are no holes on the cards and thus transfer that number together with its sign" in his description of the Calculating Engine's Store. In 1881 Jules Carpentier developed a method of recording and playing back performances on a harmonium using punched cards; the system was called the Mélographe Répétiteur and “writes down ordinary music played on the keyboard dans la langage de Jacquard”, as holes punched in a series of cards.
By 1887 Carpentier had separated the mechanism into the Melograph which recorded the player's key presses and the Melotrope which played the music. At the end of the 1800s Herman Hollerith invented the recording of data on a medium that could be read by a machine. "After some initial trials with paper tape, he settled on punched cards...", developing punched card data processing technology for the 1890 US census. His tabulating machines read and summarized data stored on punched cards and they began use for government and commercial data processing; these electromechanical machines only counted holes, but by the 1920s they had units for carrying out basic arithmetic operations. Hollerith founded the Tabulating Machine Company, one of four companies that were amalgamated to form a fifth company, Computing-Tabulating-Recording Company renamed International Business Machines Corporation. Other companies entering the punched card business included The Tabulator Limited, Deutsche Hollerith-Maschinen Gesellschaft mbH, Powers Accounting Machine Company, Remington Rand, H.
W. Egli Bull; these companies, others and marketed a variety of punched cards and unit record machines for creating and tabulating punched cards after the development of electronic computers in the 1950s. Both IBM and Remington Rand tied punched card purchases to machine leases, a violation of the 1914 Clayton Antitrust Act. In 1932, the US government took both to court on this issue. Remington Rand settled quickly. IBM viewed its business as providing a service. IBM fought all the way to the Supreme Court and lost in 1936. IBM had 32 presses at work in Endicott, N. Y. printing and stacking five to 10 million punched cards every day." Punched cards were used as legal documents, such as U. S. Government checks and savings bonds. During WW II punched card equipment was used by the Allies in some of their efforts to decrypt Axis communications. See, for example, Central Bureau in Australia. At Bletchley Park in England, 2,000,000 punched cards were used each week for storing decrypted German messages.
Punched card technology developed into a powerful tool for business data-processing. By 1950 punched cards had become ubiquitous in government. "Do not fold, spindle or mutilate," a generalized version of the warning that appeared on some punched cards, became a motto for the post-World War II era. In 1955 IBM signed a consent decree requiring, amongst other things, that IBM would by 1962 have no more than one-half of the punched card manufacturing capacity in the United States. Tom Watson Jr.'s decision to sign this decree, where IBM saw the punched card provisions as the most significant point, completed the transfer of power to him from Thomas Watson, Sr. The UNITYPER introduced magnetic tape for data entry in the 1950s. During the 1960s, the punched card was replaced as the primary means for data storage by magnetic tape, as better, more capable computers became available. Mohawk Data Sciences introduced a magnetic tape encoder in 1965, a system marketed as a keypunch replacement, somewhat successful.
Punched cards were still c
Computer data storage
Computer data storage called storage or memory, is a technology consisting of computer components and recording media that are used to retain digital data. It is a core function and fundamental component of computers; the central processing unit of a computer is. In practice all computers use a storage hierarchy, which puts fast but expensive and small storage options close to the CPU and slower but larger and cheaper options farther away; the fast volatile technologies are referred to as "memory", while slower persistent technologies are referred to as "storage". In the Von Neumann architecture, the CPU consists of two main parts: The control unit and the arithmetic logic unit; the former controls the flow of data between the CPU and memory, while the latter performs arithmetic and logical operations on data. Without a significant amount of memory, a computer would be able to perform fixed operations and output the result, it would have to be reconfigured to change its behavior. This is acceptable for devices such as desk calculators, digital signal processors, other specialized devices.
Von Neumann machines differ in having a memory in which they store their operating instructions and data. Such computers are more versatile in that they do not need to have their hardware reconfigured for each new program, but can be reprogrammed with new in-memory instructions. Most modern computers are von Neumann machines. A modern digital computer represents data using the binary numeral system. Text, pictures and nearly any other form of information can be converted into a string of bits, or binary digits, each of which has a value of 1 or 0; the most common unit of storage is the byte, equal to 8 bits. A piece of information can be handled by any computer or device whose storage space is large enough to accommodate the binary representation of the piece of information, or data. For example, the complete works of Shakespeare, about 1250 pages in print, can be stored in about five megabytes with one byte per character. Data are encoded by assigning a bit pattern to digit, or multimedia object.
Many standards exist for encoding. By adding bits to each encoded unit, redundancy allows the computer to both detect errors in coded data and correct them based on mathematical algorithms. Errors occur in low probabilities due to random bit value flipping, or "physical bit fatigue", loss of the physical bit in storage of its ability to maintain a distinguishable value, or due to errors in inter or intra-computer communication. A random bit flip is corrected upon detection. A bit, or a group of malfunctioning physical bits is automatically fenced-out, taken out of use by the device, replaced with another functioning equivalent group in the device, where the corrected bit values are restored; the cyclic redundancy check method is used in communications and storage for error detection. A detected error is retried. Data compression methods allow in many cases to represent a string of bits by a shorter bit string and reconstruct the original string when needed; this utilizes less storage for many types of data at the cost of more computation.
Analysis of trade-off between storage cost saving and costs of related computations and possible delays in data availability is done before deciding whether to keep certain data compressed or not. For security reasons certain types of data may be kept encrypted in storage to prevent the possibility of unauthorized information reconstruction from chunks of storage snapshots; the lower a storage is in the hierarchy, the lesser its bandwidth and the greater its access latency is from the CPU. This traditional division of storage to primary, secondary and off-line storage is guided by cost per bit. In contemporary usage, "memory" is semiconductor storage read-write random-access memory DRAM or other forms of fast but temporary storage. "Storage" consists of storage devices and their media not directly accessible by the CPU hard disk drives, optical disc drives, other devices slower than RAM but non-volatile. Memory has been called core memory, main memory, real storage or internal memory. Meanwhile, non-volatile storage devices have been referred to as secondary storage, external memory or auxiliary/peripheral storage.
Primary storage referred to as memory, is the only one directly accessible to the CPU. The CPU continuously reads instructions executes them as required. Any data operated on is stored there in uniform manner. Early computers used delay lines, Williams tubes, or rotating magnetic drums as primary storage. By 1954, those unreliable methods were replaced by magnetic core memory. Core memory remained dominant until the 1970s, when advances in integrated circuit technology allowed semiconductor memory to become economically competitive; this led to modern random-access memo
International Business Machines Corporation is an American multinational information technology company headquartered in Armonk, New York, with operations in over 170 countries. The company began in 1911, founded in Endicott, New York, as the Computing-Tabulating-Recording Company and was renamed "International Business Machines" in 1924. IBM produces and sells computer hardware and software, provides hosting and consulting services in areas ranging from mainframe computers to nanotechnology. IBM is a major research organization, holding the record for most U. S. patents generated by a business for 26 consecutive years. Inventions by IBM include the automated teller machine, the floppy disk, the hard disk drive, the magnetic stripe card, the relational database, the SQL programming language, the UPC barcode, dynamic random-access memory; the IBM mainframe, exemplified by the System/360, was the dominant computing platform during the 1960s and 1970s. IBM has continually shifted business operations by focusing on higher-value, more profitable markets.
This includes spinning off printer manufacturer Lexmark in 1991 and the sale of personal computer and x86-based server businesses to Lenovo, acquiring companies such as PwC Consulting, SPSS, The Weather Company, Red Hat. In 2014, IBM announced that it would go "fabless", continuing to design semiconductors, but offloading manufacturing to GlobalFoundries. Nicknamed Big Blue, IBM is one of 30 companies included in the Dow Jones Industrial Average and one of the world's largest employers, with over 380,000 employees, known as "IBMers". At least 70% of IBMers are based outside the United States, the country with the largest number of IBMers is India. IBM employees have been awarded five Nobel Prizes, six Turing Awards, ten National Medals of Technology and five National Medals of Science. In the 1880s, technologies emerged that would form the core of International Business Machines. Julius E. Pitrap patented the computing scale in 1885. On June 16, 1911, their four companies were amalgamated in New York State by Charles Ranlett Flint forming a fifth company, the Computing-Tabulating-Recording Company based in Endicott, New York.
The five companies had offices and plants in Endicott and Binghamton, New York. C.. They manufactured machinery for sale and lease, ranging from commercial scales and industrial time recorders and cheese slicers, to tabulators and punched cards. Thomas J. Watson, Sr. fired from the National Cash Register Company by John Henry Patterson, called on Flint and, in 1914, was offered a position at CTR. Watson joined CTR as General Manager 11 months was made President when court cases relating to his time at NCR were resolved. Having learned Patterson's pioneering business practices, Watson proceeded to put the stamp of NCR onto CTR's companies, he implemented sales conventions, "generous sales incentives, a focus on customer service, an insistence on well-groomed, dark-suited salesmen and had an evangelical fervor for instilling company pride and loyalty in every worker". His favorite slogan, "THINK", became a mantra for each company's employees. During Watson's first four years, revenues reached $9 million and the company's operations expanded to Europe, South America and Australia.
Watson never liked the clumsy hyphenated name "Computing-Tabulating-Recording Company" and on February 14, 1924 chose to replace it with the more expansive title "International Business Machines". By 1933 most of the subsidiaries had been merged into one company, IBM. In 1937, IBM's tabulating equipment enabled organizations to process unprecedented amounts of data, its clients including the U. S. Government, during its first effort to maintain the employment records for 26 million people pursuant to the Social Security Act, the tracking of persecuted groups by Hitler's Third Reich through the German subsidiary Dehomag. In 1949, Thomas Watson, Sr. created IBM World Trade Corporation, a subsidiary of IBM focused on foreign operations. In 1952, he stepped down after 40 years at the company helm, his son Thomas Watson, Jr. was named president. In 1956, the company demonstrated the first practical example of artificial intelligence when Arthur L. Samuel of IBM's Poughkeepsie, New York, laboratory programmed an IBM 704 not to play checkers but "learn" from its own experience.
In 1957, the FORTRAN scientific programming language was developed. In 1961, IBM developed the SABRE reservation system for American Airlines and introduced the successful Selectric typewriter. In 1963, IBM employees and computers helped. A year it moved its corporate headquarters from New York City to Armonk, New York; the latter half of the 1960s saw IBM continue its support of space exploration, participating in the 1965 Gemini flights, 1966 Saturn flights and 1969 lunar mission. On April 7, 1964, IBM announced the first computer system family, the IBM System/360, it spanned the complete range of commercial and scientific applications from large to small, allowing companies for the first time to upgrade to models with greater computing capability without having to rewrite their applications. It was followed by the IBM System/370 in 1970. Together the
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 respectively. A device that stores computer data on magnetic tape is known as a tape drive. Magnetic tape revolutionized reproduction and broadcasting, it allowed radio, which had always been broadcast live, to be recorded for or repeated airing. It allowed gramophone records to be recorded in multiple parts, which were mixed and edited with tolerable loss in quality, it was a key technology in early computer development, allowing unparalleled amounts of data to be mechanically created, stored for long periods, accessed. In recent decades, other technologies have been developed that can perform the functions of magnetic tape. In many cases, these technologies have replaced tape. Despite this, innovation in the technology continues, Sony and IBM continue to produce new magnetic tape drives.
Over time, magnetic tape made in the 1970s and 1980s can suffer from a type of deterioration called sticky-shed syndrome. It can render the tape unusable; the oxide side of a tape is the surface. This is the side that stores the information, the opposite side is a substrate to give the tape strength and flexibility; the name originates from the fact that the magnetic side of most tapes is made of iron oxide, though chromium is used for some tapes. An adhesive binder between the oxide and the substrate holds the two sides together. In all tape formats, a tape drive uses motors to wind the tape from one reel to another, passing over tape heads to read, write or erase as it moves. Magnetic tape was invented for recording sound by Fritz Pfleumer in 1928 in Germany, based on the invention of magnetic wire recording by Oberlin Smith in 1888 and 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 tended to shred the tape. Another 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, the outbreak of World War II, these developments in Germany were kept secret. Although the Allies knew from their monitoring of Nazi radio broadcasts that the Germans had some new form of recording technology, its nature was not discovered until the Allies acquired captured German recording equipment as they invaded Europe at the end of the war, it was only after the war that Americans Jack Mullin, John Herbert Orr, 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 been developed since, most reel-to-reel and Compact Cassette.
The practice of recording and editing audio using magnetic tape established itself as an obvious improvement over previous methods. Many saw the potential of making the same improvements in recording the video signals used by television. Video signals use more bandwidth than audio signals. Existing audio tape recorders could not 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 high 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 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. Improvements by other companies Sony, led 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 cartridges. Videocassette recorders used to be common in homes and television production facilities, but many functions of the VCR have been replaced with more modern technology. 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 offer improvements like random access to any scene in the recording and the ability to pause a live program and have replaced videotape in many situations. Magnetic tape was first used to record computer data in 1951 on the Eckert-Mauchly UNIVAC I; the system's UNISERVO I tape drive used a thin strip of one half inch wide metal, consisting of nickel-plated bronze. Recording density was 100 characters per inch on eight tracks. Early IBM 7 track tape drives were floor-standing and used vacuum columns to mechanically 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 used to represent "the computer" in movies and televis