1946: Williams demonstrates CRT storage

Cathode Ray Tube electrostatic effect enables random access memory

Aware of work in the U.S. on electrostatic memory effects on the screen of a cathode ray tube (CRT), Fredrick C. Williams (1911-1977) demonstrated the storage of a single binary digit (bit) at the British Telecommunications Research Establishment in October 1946. Storage occurs where a dot drawn on a cathode ray tube (CRT) screen induces a positive charge surrounded by a negatively charged area. A positive voltage pulse induced in a metal plate placed at the face of the tube enables reading of the stored information. The electron beam can be directed to any location on the screen thus offering random access to the data but as charge gradually leaks away from the site it must be rewritten on a regular cycle.

Williams moved to Manchester University where working with Tom Kilburn in late 1947 they were able to store 2,048 bits. In 1948 the Manchester “Baby” machine ran the first program on an electronic stored-program computer using Williams-Kilburn Tube storage. Application in early U.S. machines included the Princeton IAS, IBM 701, IBM 702, Standards Western Automatic Computer (SWAC), and UNIVAC 1103, as well as the Soviet Strela-1 and the Japanese TAC (Tokyo Automatic Computer).

British-born engineer Jan A. Rajchman designed the Solectron special-purpose vacuum tube for RCA in 1946. The device worked on the same principle as the Williams-Kilburn Tube but was intended to improve on its predictability of operation. Designed to hold 4096 bits, it proved difficult to build and was replaced by a smaller 256-bit version that was used on the RAND Corporation JOHNNIAC before being replaced by magnetic core memory. Similar technologies of electron beam addressable memories (BEAM OS) were pursued by GE in the mid 1970’s for military applications that were not compatible with mechanically moving storage.

  • Williams, Frederick C. & Tom Kilburn. “Improvements in or relating to electrical information-storing means” U.K. Patent 645,691(Filed: Dec 11, 1946 Issued: Nov 8, 1950)
  • Williams, Frederick C. “Improvements in or relating to electrical storage apparatus” U.K. Patent 657,591 (Filed: Oct 2, 1947 Issued: Aug 9, 1951)
  • Hartree, D.R., et al. "A Discussion on Computing Machines" Proc. Royal Soc. A. (Vol. 195, 1948) pp. 265-287
  • Williams, F.C. "Cathode Ray Storage" in Wilkes, M.V., ed., Report on a Conf. on High Speed Automatic Computing Machines, Univ. Math. Lab., Cambridge, U.K. (July 22-25, 1949)
  • Rajchman, J. A. “Electronic discharge device” U.S. Patent 2,494,670 (Filed: Apr 26, 1946 Issued: Jan 17, 1950 )
  • “BEAM OS - A new electron beam digital memory device” Electron Devices Meeting, 1975 International (Date of Conference:1-3 Dec. 1975) pp. 305 – 308
  • "F.C. Williams interview by C. Evans" The Pioneers of Computing: An Oral History of Computing Science Museum, London (1976)
  • "Dr. Jan Rajchman, an oral history conducted by Mark Heyer and Al Pinksy," IEEE History Center, Hoboken, NJ, USA (1975)

File name: 1946_CRT_v4
Rev: 9.17.15