IBM 701 Electronic Data Processing Machine

What the 701 was

The IBM 701 Electronic Data Processing Machine was IBM's first electronic computer, and it was built as a general-purpose device rather than for a single fixed function ^[1]. That distinction matters. A machine dedicated to one job has its behaviour fixed by its wiring; a general-purpose machine reads a stored program and follows it, so the same hardware can be turned to a different problem by changing the instructions. IBM says the 701 ran some 25 to 50 times faster than its predecessors and that it inaugurated the 700 series ^[1].

Where it came from

Work on the machine began in early 1951, on the third floor of a tie factory in Poughkeepsie, New York, with a team of more than 150 engineers ^[1]. For a while it carried two names: the project was first known as the Defense Calculator, and the official designation was the IBM Model 701 Electronic Data Processing Machine ^[1]. In April 1952 Thomas J. Watson announced the new machine to IBM shareholders ^[1]. Interest came quickly: by the following month ten governmental and defence customers had placed orders, and within a few months the number rose to nearly twenty ^[1].

How it was put together

The finalised machine comprised eleven connected units and used three storage methods ^[1]. The fastest was a set of Williams tubes, which held the equivalent of 20,000 digits ^[1]; a Williams tube is a cathode-ray tube whose screen stores a pattern of charged spots that the machine reads back as bits. Behind the tubes sat magnetic drums, holding as many as 82,920 digits ^[1] — a rotating magnetic surface with more room than the tubes but a longer wait to reach any given item. The third method was magnetic tape, at 8 million digits per reel ^[1]: very large capacity, but read in sequence, so it served as bulk storage rather than as the working memory of a running calculation.

Speed was quoted in raw arithmetic: more than 16,000 addition or subtraction operations and more than 2,000 multiplication or division operations per second ^[1].

What it was used for

The workload was scientific and engineering work. Applications ranged from aerodynamic measurements and rocket engine designs to studies of the nitrogen molecule ^[1]. Among the customers were the US Department of Defense and the United States Weather Bureau ^[1]. The very last 701 produced was received by the Department of Defense, in 1955 ^[1] — the same kind of customer that had formed the first orders.

Why it matters

The 701 is the point at which IBM moved into electronic computing: it made history as the company's first electronic computer ^[1]. Just as important is how it was conceived. Because it was general purpose rather than a one-off instrument for a single calculation ^[1], the machine could be applied across a range of scientific problems, from airflow to molecular structure, and the same design could be sold to different kinds of customers. The order book reflected that breadth, with governmental, defence and weather customers among the early buyers ^[1]. Its speed, roughly 25 to 50 times that of earlier machines ^[1], set the standard the next machines would be measured against, and its launch began the 700 series that followed it at IBM ^[1].