Drum memory
Computer memory and Computer data storage types |
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Volatile |
Non-volatile |
Drum memory was a magnetic
Many early computers, called drum computers or drum machines, used drum memory as the main working memory of the computer.
Drums were displaced as primary computer memory by magnetic
Technical design
A drum memory or drum storage unit contained a large metal cylinder, coated on the outside surface with a
In November 1953 Hagen published a paper disclosing "air floating" of magnetic heads in an experimental sheet metal drum.[5] 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."[6] 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 the device.
- Blocks took up an entire track and were addressed by track.
- Tracks were divided into fixed length sectors and addressing was by track and sectors.
- Blocks were variable length, and blocks were addressed by track and record number.
- Blocks were variable length with a key, and could be searched by key content.
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 the head over the desired track (
History
Tauschek's original drum memory (1932) had a capacity of about 500,000 bits (62.5 kilobytes).[2]
One of the earliest functioning computers to employ drum memory 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
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 the default virtual memory (swap) device, deriving from the use of drum secondary-storage devices as backup storage for pages in virtual memory.[11]
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.
See also
- CAB 500
- Carousel memory (magnetic rolls)
- Karlqvist gap
- Manchester Mark 1
- Random-access memory
- Wisconsin Integrally Synchronized Computer
References
- ^ US Patent 2,080,100 Gustav Tauschek, Priority date August 2, 1932, subsequent filed as German Patent DE643803, "Elektromagnetischer Speicher für Zahlen und andere Angaben, besonders für Buchführungseinrichtungen" (Electromagnetic memory for numbers and other information, especially for accounting institutions)
- ^ a b Universität Klagenfurt (ed.). "Magnetic drum". Virtual Exhibitions in Informatics. Archived from the original on 14 April 2022. Retrieved 2011-08-21.
- ^ Datamation, September 1967, p.25, "For Bendix and Ramo-Wooldridge, the G-20 and RW-400 were parallel core machines rather than serial drum machines of the type already in their product lines."
- ^ Matick, Richard (1977). Computer Storage Systems & Technology. Wiley. p. 15.
- ^ Hagen, Glenn E. (1953-11-01). Computers and Automation 1953-11: Vol 2 Iss 8. Internet Archive. Berkeley Enterprises. pp. 23, 25.
- ^ Baumeister, H (December 2, 1958). "US Patent 2,862,781 RECORDING SUPPORT DEVICES" (PDF). Retrieved July 1, 2023.
- ^ SOAP II - Symbolic Optimal Assembly Program for the IBM 650 Data Processing System (PDF), IBM, 24-4000-0
- ^ ISBN 0-7803-4709-9.
- S2CID 14861159.
- ^ Gray, George T.; Smith, Ronald Q. (October 2004). "Sperry Rand's First-Generation Computers, 1955–1960: Hardware and Software". IEEE Annals of the History of Computing: 23.
There was a 1,070-word drum memory for data, stored as twelve 6-bit digits or characters per word
- ^ "FreeBSD drum(4) manpage". Retrieved 2013-01-27.
External links
- The Story of Mel: the classic story about one programmer's drum machine hand-coding antics: Mel Kaye.
- Librascope LGP-30: The drum memory computer referenced in the above story, also referenced on Librascope LGP-30.
- Librascope RPC-4000: Another drum memory computer referenced in the above story
- Oral history interview with Dean Babcock