In 1948 IBM produced the 604 Electronic Calculating Punch. Based on vacuum-tube technology, and programmed by making wired connections on a plugboard, the mass-produced CPC 604 featured the industry’s first assemblage of digital electronics replaceable as a unit. It has been characterized a kind of an electronic version of the relay-based Pluggable Sequence Relay Calculator.
The 604 was a programmable electronic unit record machine, or punched card processor, that could perform multiple calculations, including division. It could read a punched card from a deck, do some calculations based on the wiring of its plugboard, and punch results on the same card. It could execute a program of up to 60 steps. The separate IBM 521 Card Read/Punch processed the cards and had its own plugboard which, according following the way directions were plugged, selected the columns to be read and those to be punched.
The 604 performed addition, subtraction, multiplication, and division hundreds of times faster than any of IBM's earlier electromechanical or relay-based machines, and was the first IBM product to use modular vacuum-tube based pluggable units, later used in IBM's NORC and 701 computers. Footprint: 53 by 33 inches; contained 1100 vacuum tubes and 125 relays. Power consumption 7.59 Kva. Weight: 1949 pounds. More than 5000 were sold (or, rather, rented at $645 per month, 1948 dollars, for the 604 and 521).