Selectron tube

The Selectron was an early form of digital computer memory developed by Jan A. Rajchman and his group at the Radio Corporation of America under the direction of Vladimir Zworykin. It was a vacuum tube that stored digital data as electrostatic charges using technology similar to the Williams tube storage device. The team was never able to produce a commercially viable form of Selectron before core memory became almost universal, and it remains practically unknown today.

Development of Selectron started in 1946 at the behest of John von Neumann of the Institute for Advanced Study, who was in the midst of designing the IAS machine and was looking for a new form of high-speed memory. RCA responded with the Selectron with a capacity of 4096 bits, with a planned production of 200 by the end of the year. They found the device to be much more difficult to build than expected, and they were still not available by the middle of 1948. As development dragged on, the IAS machine was forced to switch to Williams tubes for storage, and the primary customer for Selectron disappeared.

RCA continued work on the concept, re-designing it for a smaller 256-bit capacity. The 256-bit Selectron was projected to cost about $500 each when in full production. While they were more reliable and faster than the Williams tube, that cost and the lack of availability, meant they were used only in one computer: the RAND Corporation's JOHNNIAC.

Both the Selectron and the Williams tube were superseded in the market by the more compact and cost effective magnetic core memory, in the early 1950s.

The Williams tube was an example of a general class of cathode ray tube (CRT) devices known as storage tubes.

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