The IBM 604 Electronic Calculating Punch was IBM's first major foray into electronic computing. (It was preceded by the 603 Electronic Multiplier, produced in a limited run of 100; the 604 was already underway at the time, and it was seen as a better alternative for a long-term product.)
First shipped in the fall of 1948, it did much to 'school' IBM in manufacturing and supporting electronic gear; all previous IBM products had been electro-mechanical.
Controlled by a plugboard (similar to those in earlier electro-mechanical units), it could execute twenty (optionally forty; soon upped to sixty) operations on each card which it read, and had limited conditional branching, based on input data.
Available operations included division as well as multiplication; the clock was upped from the 35 KHz of the 603 to 50 Khz, to allow the maximum number of steps to be completed during a card read cycle.
It was built out of 'pluggable units', which contained a vacuum tube and its associated resistors and capacitors, an early application of modularization. The number of different types of pluggable units was strictly controlled, to ease both design and maintenance. The complete unit contained 1400 tubes, but the pluggable units contributed to ease of diagnosis, via the later-common diagnostic technique of module swapping.
Its layout was designed to occupy space, not a simple planar layout (as was common at the time) to minimize the size of the complete unit.
A great deal of work was required on IBM's part to improve the quality of the electrical and electronic components, in order to produce a reliable system.
They were produced at a rate of over 1,000 per year for several years; a total of more than 5,600 were built over the total ten-year production run.
- Charles J. Bashe, Lyle R. Johnson, John H. Palmer, Emerson W. Pugh, IBM's Early Computers, MIT Press, Cambridge, 1986