IBM 604 Calculator

The 604 calculator and the Type 521 Reader / Punch were used together. The 521 served as the input / output device, while the 604 was the "computer." When introduced, the word computer still referred to people.

The 604 is not considered a computer today. Although it was programmable, the program was stored on a plug board and not in electronic storage. The 521 punch was also programmable, but only insofar as choosing card colums to aggregate. The 604 plugboard was used to program what sorts of calculations to perform on the data fed into it by the 521. Output was then sent from the 604 back to the 521 to be punched onto cards. Below is an example of a plug board with a some program hard wired.

The 604 used pluggable units. These were typically, although not always, a single vacuum tube and associated circuitry. Pluggable units were desiged to be replaced as a unit for easier debugging and maintenance.

Below is a picture of some pluggable units of the type used in the 604.

The Gallery of Old Iron has an original CE (Customer Engineer) Manual of Instruction. In it, the picture of the 604 is simpler than the picture at the top of this page, which is probably a later model. In this picture, the 604 has only two external indicator lamps (for AC and DC power!).

The same CE manual goes into great detail of the wiring of each pluggable unit. Below is p.67.

And finally, the 604 assembly line!

The 604 calculator frame alone, without the Type 521 punch, weighed nearly 2000 lbs! The Gallery knows this, because we had to calculate shipping costs for one (alas we did not acquire it, but not because of shipping cost).