magnetic drum
<<< - >>>
The emerging computer industry saw magnetic recording as a solution to the problems of data storage and speed. In 1937, Victor Atanasoff considered a variation of Poulsen's magnetic drum as a possible memory device for his early ABC electronic computer. However, he could not afford the vacuum tubes necessary to amplify the magnetic pulses, and decided to use non-magnetic capacitors on the drum. In 1947, William C. Morris led a group of engineers at Engineering Research Associates (ERA) in Minneapolis that had worked on Project Goldberg for the Navy to develop a computer that could solve cryptographic problems. They built the first magnetic drum out of recording tape from a captured German Magnetophone recorder and heads from a Brush wire recorder. The strips of tape would not stick to the aluminum drum, so they spray-painted an iron oxide emulsion obtained from 3M in Minneapolis directly onto the surface of the drum. John Coombs reported their success at the Chicago National Electronics Conference in November 1947. The drum was 5 inches in diameter and revolved at 3000 rpm, recording at a density of 230 bits per inch with a rigid head mounted only .001 inch from the surface of the drum. Howard Aiken at Harvard was also experimenting with a magnetic drum on the Mark II computer in 1947, and he would make the drum the key feature of his improved Mark III computer in 1948. Harry Huskey would use a magnetic drum in this design of the Standards Eastern Automatic Computer for the National Bureau of Standards in 1948. Arnold D. Booth in Britain built a magnetic drum for the Automatic Relay Computer in 1948 and would install a drum in the Manchester "baby" computer in 1949. The ERA would build the Atlas computer in 1948 with a magnetic drum 8.5 inches in diameter with 200 read/write heads and a capacity of 16,384 words of 24-bit length. The ERA would patent its drum design in 1948, including the so-called "sprocket track" that was a control track to map the addresses of data in the storage tracks. The access speed and large capacity of magnetic drums exceeded all other forms of computer memory in use during the decade after World War II, such as the CRT and the mercury delay line. It would remain the preferred computer memory until the faster magnetic core devices became available in the late 1950s.

Evolution of the Computer
Museum of American Heritage in Palo Alto
Computer History Museum in Mountain View