Drum memory

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For the electronic musical instrument, see drum machine. Drum memory_sentence_0

Drum memory was a magnetic data storage device invented by Gustav Tauschek in 1932 in Austria. Drum memory_sentence_1

Drums were widely used in the 1950s and into the 1960s as computer memory. Drum memory_sentence_2

For many early computers, drum memory formed the main working memory of the computer. Drum memory_sentence_3

It was so common that these computers were often referred to as drum machines. Drum memory_sentence_4

Some drum memories were also used as secondary storage. Drum memory_sentence_5

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. Drum memory_sentence_6

Drums in turn were replaced by hard disk drives for secondary storage, which were both less expensive and offered denser storage. Drum memory_sentence_7

The manufacturing of drums ceased in the 1970s. Drum memory_sentence_8

Technical design Drum memory_section_0

A drum memory contained a large metal cylinder, coated on the outside surface with a ferromagnetic recording material. Drum memory_sentence_9

It could be considered the precursor to the hard disk drive (HDD), but in the form of a drum rather than a flat disk. Drum memory_sentence_10

In most designs, one or more rows of fixed read-write heads ran along the long axis of the drum, one for each track. Drum memory_sentence_11

The drum's controller simply selected the proper head and waited for the data to appear under it as the drum turned (rotational latency). Drum memory_sentence_12

Not all drum units were designed with each track having its own head. Drum memory_sentence_13

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. Drum memory_sentence_14

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 the head over the desired track (seek time). Drum memory_sentence_15

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. Drum memory_sentence_16

They did this by timing how long it would take after loading an instruction for 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. Drum memory_sentence_17

This method of timing-compensation, called the "skip factor" or "interleaving" (interleaving in disk storage), was used for many years in storage memory controllers. Drum memory_sentence_18

History Drum memory_section_1

Tauschek's original drum memory (1932) had a capacity of about 500,000 bits (62.5 kilobytes). Drum memory_sentence_19

One of the earliest functioning computers to employ drum memory was the Atanasoff–Berry computer (1942). Drum memory_sentence_20

It stored 3,000 bits; however, it employed capacitance rather than magnetism to store the information. Drum memory_sentence_21

The outer surface of the drum was lined with electrical contacts leading to capacitors contained within. Drum memory_sentence_22

Magnetic drums were developed for the U.S. Drum memory_sentence_23 Navy during World War II with the work continuing at Engineering Research Associates (ERA) in 1946 and 1947. Drum memory_sentence_24

An experimental ERA study was completed and reported to the Navy on June 19, 1947. Drum memory_sentence_25

Other early drum storage device development occurred at Birkbeck College (University of London), Harvard University, IBM and the University of Manchester. Drum memory_sentence_26

An ERA drum was the internal memory for the ATLAS-I computer delivered to the U.S. Navy in October 1950. Drum memory_sentence_27

Through mergers, ERA became a division of UNIVAC shipping the Series 1100 drum as a part of the UNIVAC File Computer in 1956; each drum stored 180,000 characters. Drum memory_sentence_28

The first mass-produced computer, the IBM 650, had about 8.5 kilobytes of drum memory (later doubled to about 17 kilobytes in the Model 4). Drum memory_sentence_29

As late as 1980, PDP-11/45 machines using magnetic core main memory and drums for swapping were still in use at many of the original UNIX sites. Drum memory_sentence_30

In BSD Unix and its descendants, /dev/drum was the name of the default virtual memory (swap) device, deriving from the use of drum secondary-storage devices as backup storage for pages in virtual memory. Drum memory_sentence_31

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. Drum memory_sentence_32

See also Drum memory_section_2

Drum memory_unordered_list_0

Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/Drum memory.