Most of the circuitry was based on modifications of circuit designs used in the earlier 603 Electronic Multiplier and was packaged in small one tube replaceable standardized modules. Clock speed was increased from the 603's rate of 35kHz to 50kHz. It performed fixed point addition, subtraction, multiplication and division using Binary coded decimal. Initial versions supported 40 program steps, but this was soon expanded to 60. Processing was still locked to the reader/punch cycle time, thus program execution had to complete within the time between a card leaving the read station and entering the punch station!
In 1949 a modified version of the 604, connected to an accounting machine, was introduced as the Card Programmed Electronic Calculator. This machine read its program steps from punch cards instead of a plug-board.
See also: List of IBM products.