In net terms, the development requirement underlying the 650 was for a small, reliable machine offering the versatility of a stored-program computer that could operate within the traditional punched card environment. IBM -- and the industry -- wanted a machine capable of performing arithmetic, storing data, processing instructions and providing suitable read-write speeds at reasonable cost. The magnetic drum concept was seen as the answer to the speed and storage problems.
Data and instructions were stored in the form of magnetized spots on the surface of a drum four inches in diameter and 16 inches long, which rotated 12,500 times a minute. The drum memory could hold 20,000 digits at 2,000 separate "addresses."
Information was entered from punched cards at the rate of 200 a minute or manually from the operator's console. Computation results were produced on punched cards at a maximum rate of 100 a minute.
The 650 had a "table look up" feature that permitted automatic searching of rate tables used in the utilities, life and casualty insurance, and transportation and other industries. The system could thus select the applicable rate for any given type of service, calculate the bill amount and punch the result on a card with other information needed for bill preparation. In such applications, the 650's comprehensive error-detecting circuitry permitted self-checking and eliminated the need for separate processing of cards for checking purposes.
In 1955 technological advancements from the 700 series of computers directly benefited the 650. Magnetic tape input and output and a directly coupled printer -- the IBM 407 accounting machine -- became available as additional equipment for the 650.
The IBM 650 -- a machine developed for "ordinary business" -- went on to become the most popular computer of the 1950s.
You can visit the 650 Reference room to see and learn more about this landmark IBM product.