The Selectron was an early form of digital computer memory developed by Jan A. Rajchman and his group at the Radio Corporation of America (RCA) under the direction of Vladimir K. 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 magnetic-core memory became almost universal. Development 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's original design concept had a capacity of 4096 bits, with a planned production of 200 by the end of 1946. 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 lost interest in the design and assigned its engineers to improve televisions A contract from the US Air Force led to a re-examination of the device in a 256-bit form. Rand Corporation took advantage of this project to switch their own IAS machine, the JOHNNIAC, to this new version of the Selectron, using 80 of them to provide 512 40-bit words of main memory. They signed a development contract with RCA to produce enough tubes for their machine at a projected cost of $500 per tube ($ in ). Around this time IBM expressed an interest in the Selectron as well, but this did not lead to additional production. As a result, RCA assigned their engineers to color television development, and put the Selectron in the hands of "the mothers-in-law of two deserving employees (the Chairman of the Board and the President)." Both the Selectron and the Williams tube were superseded in the market by the compact and cost-effective magnetic-core memory, in the early 1950s. The JOHNNIAC developers had decided to switch to core even before the first Selectron-based version had been completed. Principle of operation Electrostatic storage The Williams tube was an example of a general class of cathode ray tube (CRT) devices known as storage tubes. The primary function of a conventional CRT is to display an