Professor Frederick C. Williams and colleagues at Manchester University in the United Kingdom developed the first random access computer memory, through using electrostatic cathode-ray display tubes as digital stores. By 1948, a storage of 1024 bits was successfully implemented. William's colleague Tom Kilburn made improvements that increased the capacity to 2048 bits. The Williams-Kilburn tubes (commonly known as Williams tubes) were used on several of the early stored program computers, including the Manchester 'Baby' (1948) and the Manchester Mark I which became operational in 1949, and the Institute of Advanced Study (IAS) machine spearheaded by von Neumann at Princeton, finally completed in 1951. The big advantage of the Williams tube memory was that it allowed fast random access (any memory location could be addressed and read directly). The Manchester Mark I was the first to store both its programs and data in RAM, as modern computers do.
The Selectron tube was an early form of computer memory developed by RCA (Radio Corporation of America). Like the Williams-Kilburn tube, the Selectron was also a random access storage device. Development started in 1946 with a planned production of 200 by the end of the year, but production problems meant that they were still not available by the middle of 1948. By that time their primary customer, John von Neumann's IAS machine, was forced to switch to the Williams-Kilburn tube for storage, and RCA eventually had to scale down the Selectron from storing 4096 bits, to 256. This smaller version saw use in a number of IAS-related machines, but finally RCA gave up on the concept.