RCA SB-256 256-bit production Selectron
Selective Electrostatic Storage Tube
Tube à mémoire
Selectron 256-Bit Digitale Speicherröhre
The Selectron was an early form of digital computer memory developed by Jan A. Rajchman at RCA.
In some documents, this tube is designated SE256.
About 200 256-bit “production” tubes were produced in the early 1950s.
The AFCRC (Air Force Cambridge Research Center) Memory System, designed and built by the staff at RCA
Laboratories in Princeton, used 20 SB-256 Selectrons.
The JOHNNIAC (short for John v. Neumann Numerical
Integrator and Automatic Computer) built by RAND in 1953
used 40 Selectrons for its fast access memory, but they were replaced by core memory in March 1955.
The magnetic-core memory, which emerged in 1953, sounded the death knell of the Selectron tube.
Everything you may want to know about the SELECTRON has been gathered by Charles S. Osborne on his website:
The RCA Selectron: A 1940s vacuum tube digital memory
Picture of the Johnniac under construction with Selectron tubes:
Computer History Museum
Fiche technique • Data sheet • Datenblatt:
• Jan Rajchman, The Selectron (Proceedings of a Second Symposium on Large-Scale Digital Calculating Machinery).
• Electronic Memory Tube SB-256, RCA Research Report, 1949.
Hauteur • Height • Höhe : 240 mm • 9" 4/10
Diamètre • Diameter • Durchmesser : 76 mm • 3"
Poids • Weight • Gewicht : 860 g • 1.90 lbs
The number P990-4 is manually etched on the bulb
From US Patent 2,604,606 (Filed Oct. 15, 1949)
From Max Knoll and Benjamin Kazan, Storage Tubes and Their Basic Principles, 1952
Magnetic-Core Memory from Burroughs E4000 Accounting System (detail)
Dynamic life test equipment for SB-256 storage tubes
(from RCA Research Report, 1949)
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