<- Virtual Exhibitions in Informatics

Williams-Kilburn tube


Williams-Kilburn tube

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.


Internal Links:
Delay line memory
Core memory

References:
http://ed-thelen.org/comp-hist/TheCompMusRep/TCMR-V19.html
http://www.routledge-ny.com/ref/20ctech/computer.html

Selectron tube


Selectron tube

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.
The original 4096-bit Selectron was a large (5 inch by 3 inch) vacuum tube with a cathode running up the middle, surrounded by two separate sets of wires forming a cylindrical grid, a dielectric material outside of the grid, and finally a cylinder of metal conductor outside the dielectric, called the signal plate.
The smaller capacity 256-bit system was constructed similarly, but built in a planar fashion rather than cylindrical,resulting in an even larger vacuum tube. Each one cost about $500 to build, and while they were more reliable and faster than the Williams-Kilburn tube, their cost meant they were used only on a few machines.Both systems were replaced in the market with core memory, as soon as that became widely available.

Internal Links:
Delay line memory

Core memory

References:
http://en.wikipedia.org/wiki/Selectron_tube
http://www.computer50.org/mark1/moore.school/selectron.html