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26-448: When the Mark I started running in 1951, reliability was poor. The primary concern was the drum memory system, which broke down all the time. Additionally, the machine used 4,200 thermionic valves , mostly EF50 pentodes and diodes that had to be replaced constantly. The Williams tubes, used as random-access memory and registers, were reliable but required constant maintenance. As soon as

52-539: A 10-bit short word, the system required virtually no maintenance, considerably more important for commercial users. 1024×40-bits of core were provided, backed by four drums each holding 4096×40-bits. The first of an eventual 19 Mercury computers was delivered in August 1957. Manchester University received one in February 1958, leasing half the time to commercial users via Ferranti's business unit. Both CERN at Geneva and

78-530: A 30-bit mantissa, and another as a 10-bit exponent. It could add two floating-point numbers in about 180 microseconds, and multiply them in about 360 microseconds. Ferranti, which had built the Mark I for the university, continued development of the prototype Meg to produce the Mercury. The main change was to replace the Williams tubes with core memory. Although slower to access, at about 10 μs for

104-469: A head-per-track access mechanism and a capacity of 4 MB. The 2301 has 800 physical tracks; four physical tracks make up one logical track which is read or written as a unit. The 200 logical tracks have 20,483 bytes each. The average access time is 8.6 ms, and the data transfer rate is 1,200,000 bytes per second. The 2301 attaches to a System/360 via a selector channel and an IBM 2820 Storage Control Unit, which can control up to four 2301 units. The IBM 2303

130-473: A mix of 7320 and 1301 DASD. One or two 7631 controllers can attach to a computer system, but the system can still attach only a total of five DASD. When used with a 709x, a track holds 2,796 6-bit characters, and a 7320 unit holds 1,118,400 characters. Data transfer rate is 202,800 characters per second. The 7320 attaches to a System/360 through a channel and an 2841 Storage Control unit. Each 2841 can attach up to eight 7320 devices. When used with System/360,

156-578: A paper disclosing "air floating" of magnetic heads in an experimental sheet metal drum. A US patent filed in January 1954 by Baumeister of IBM disclosed a "spring loaded and air supported shoe for poising a magnetic head above a rapidly rotating magnetic drum." Flying heads became standard in drums and hard disk drives . Magnetic drum units used as primary memory were addressed by word. Drum units used as secondary storage were addressed by block. Several modes of block addressing were possible, depending on

182-485: A track holds 2,081 8-bit bytes, and a 7320 unit holds 878,000 bytes. Data transfer rate is 135,000 bytes per second. The 7320 was superseded by the IBM 2301 in mid-1966. The IBM 2301 is a magnetic drum storage device introduced in the late 1960s to "provide large capacity, direct access storage for IBM System/360 Models 65, 67, 75, or 85." The vertically mounted drum rotates at around 3,500 revolutions per minute, and has

208-401: The 700/7000 series and System/360 series of computers. The IBM 731 is a discontinued storage unit used on the IBM 701 . It has a storage capacity of 2,048 36-bit words (9,216 8-bit bytes). The IBM 732 is a discontinued storage unit used on the IBM 702 . It has a storage capacity of 60,000 6-bit characters (45,000 8-bit bytes). The IBM 733 is a discontinued storage unit used on

234-633: The Atomic Energy Research Establishment at Harwell also installed theirs in 1958. A Mercury bought in 1959 was the UK Met Office 's first computer. The University of Buenos Aires in Argentina received another one in 1960. The machine could run Mercury Autocode, a simplified coding system of the type later described as a high-level programming language . Detailed information both about the Mercury hardware and

260-553: The Autocode coding system is included in a downloadable Spanish-language Autocode manual. Mercury weighed 2,500 pounds (1.3 short tons; 1.1 t). Drum memory Drum memory was a magnetic data storage device invented by Gustav Tauschek in 1932 in Austria . Drums were widely used in the 1950s and into the 1960s as computer memory . Many early computers, called drum computers or drum machines, used drum memory as

286-406: The IBM 704 and IBM 709 . It has a storage capacity of 8192 36-bit words (36,864 8-bit bytes). The IBM 734 is a discontinued storage unit used on the IBM 705 It has a storage capacity of 60,000 6-bit characters (45,000 8-bit bytes). The IBM 7320 is a discontinued storage unit manufactured by IBM announced on December 10, 1962 for the IBM 7090 and 7094 computer systems, was retained for

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312-442: The 1970s. A drum memory or drum storage unit contained a large metal cylinder, coated on the outside surface with a ferromagnetic recording material. It could be considered the precursor to the hard disk drive (HDD), but in the form of a drum (cylinder) rather than a flat disk. In most designs, one or more rows of fixed read-write heads ran along the long axis of the drum, one for each track. The drum's controller simply selected

338-506: The Mark I's 25 kW to the Meg's 12 kW. Like the Mark I, Meg was based on a 10-bit "short word", combining two to form a 20-bit address and four to make a 40-bit integer. This was a result of the physical properties of the Williams tubes, which were used to make eight B-lines , or in modern terminology, accumulator / index registers . Meg could multiply two integers in about 60 microseconds. The floating-point unit used three words for

364-690: The Navy on June 19, 1947. Other early drum storage device development occurred at Birkbeck College ( University of London ), Harvard University , IBM and the University of Manchester . An ERA drum was the internal memory for the ATLAS-I computer delivered to the U.S. Navy in October 1950 and later sold commercially as the ERA 1101 and UNIVAC 1101 . Through mergers , ERA became a division of UNIVAC shipping

390-578: The Series 1100 drum as a part of the UNIVAC File Computer in 1956; each drum stored 180,000 6-bit characters (135 kilobytes). The first mass-produced computer, the IBM 650 (1954), initially had up to 2,000 10-digit words, about 17.5 kilobytes , of drum memory (later doubled to 4,000 words, about 35 kilobytes, in the Model 4). In BSD Unix and its descendants, /dev/drum was the name of

416-443: The computer to be ready to read the next one, then placing that instruction on the drum so that it would arrive under a head just in time. This method of timing-compensation, called the "skip factor" or " interleaving ", was used for many years in storage memory controllers. Tauschek's original drum memory (1932) had a capacity of about 500,000 bits (62.5 kilobytes ). One of the earliest functioning computers to employ drum memory

442-610: The default virtual memory (swap) device, deriving from the historical use of drum secondary-storage devices as backup storage for pages in virtual memory . Magnetic drum memory units were used in the Minuteman ICBM launch control centers from the beginning in the early 1960s until the REACT upgrades in the mid-1990s. IBM drum storage In addition to the drums used as main memory by IBM, e.g., IBM 305 , IBM 650 , IBM offered drum devices as secondary storage for

468-411: The device. Some devices were divided into logical cylinders, and addressing by track was actually logical cylinder and track. The performance of a drum with one head per track is comparable to that of a disk with one head per track and is determined almost entirely by the rotational latency, whereas in an HDD with moving heads its performance includes a rotational latency delay plus the time to position

494-479: The earliest System/360 systems as a count key data device, and was discontinued in 1965. The 7320 is a vertically mounted head-per-track device with 449 tracks, 400 data tracks, 40 alternate tracks, and 9 clock/format tracks. The rotational speed is 3,490 rpm, so the average rotational delay is 8.6 milliseconds. Attachment to a 709x system is through an IBM 7909 Data Channel and an IBM 7631 File Control unit, which can attach up to five random-access storage units,

520-450: The head over the desired track ( seek time ). In the era when drums were used as main working memory, programmers often did optimum programming —the programmer—or the assembler, e.g., Symbolic Optimal Assembly Program (SOAP)—positioned code on the drum in such a way as to reduce the amount of time needed for the next instruction to rotate into place under the head. They did this by timing how long it would take after loading an instruction for

546-405: The main designers of the Mark I, started with a design very similar to the Mark I but replacing valves used as diodes with solid-state diodes. These were much less expensive than transistors, yet enough of them were used in the design that replacing just the diodes would still result in a significant simplification and improvement in reliability. At that time computers were used almost always in

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572-599: The main working memory of the computer. Some drums were also used as secondary storage as for example various IBM drum storage drives and the UNIVAC FASTRAND series of drums. Drums were displaced as primary computer memory by magnetic core memory , which offered a better balance of size, speed, cost, reliability and potential for further improvements. Drums were then replaced by hard disk drives for secondary storage , which were both less expensive and offered denser storage. The manufacturing of drums ceased in

598-543: The proper head and waited for the data to appear under it as the drum turned ( rotational latency ). Not all drum units were designed with each track having its own head. Some, such as the English Electric DEUCE drum and the UNIVAC FASTRAND had multiple heads moving a short distance on the drum in contrast to modern HDDs, which have one head per platter surface. In November 1953 Hagen published

624-461: The sciences, and they decided to add a floating-point unit to greatly improve performance in this role. Additionally the machine was to run at 1 MHz, eight times faster than the Mark I's 125 kHz, leading to the use of the name megacycle machine, and eventually Meg. Meg first ran in May 1954. The use of solid-state diodes reduced valve count by well over half, reducing the power requirement from

650-592: The system went into operation, teams started looking at solutions to these problems. One team decided to produce a much smaller and more cost-effective system built entirely with transistors . It first ran in November 1953 and is believed to be the first entirely transistor-based computer. Metropolitan-Vickers later built this commercially as the Metrovick 950 , delivering seven. At the time, transistors were very expensive, compared to tubes. Another team, including

676-485: Was the Atanasoff–Berry computer (1942). It stored 3,000 bits; however, it employed capacitance rather than magnetism to store the information. The outer surface of the drum was lined with electrical contacts leading to capacitors contained within. Magnetic drums were developed for the U.S. Navy by Engineering Research Associates (ERA) in 1946 and 1947. An experimental ERA study was completed and reported to

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