Discovery · University of Pennsylvania, Philadelphia · 1946

The Giant Computer Needed Six Women to Tell It What to Do

The machine filled a room. Its instructions depended on work the headlines often overlooked.

1. The word computer meant a person too

During the Second World War, teams of people performed difficult numerical calculations for military work. Many were women employed as human computers. At the University of Pennsylvania, a project sought to carry out such calculations electronically at unprecedented speed. The machine that emerged was ENIAC, but building the hardware did not automatically tell it how to solve a useful problem.

The electronic computer still needed people who understood the computation.

2. A machine on a room-sized scale

Developed under John Mauchly and J. Presper Eckert with Army funding, ENIAC used thousands of vacuum tubes and occupied a large space. Its speed was extraordinary compared with manual calculation. Yet it was not a modern laptop enlarged into cabinets. Its original operation required physical configuration, and changing a problem could involve switches, cables and detailed knowledge of how the units interacted.

The calculation could be fast while preparing it remained painstakingly physical.

3. Six programmers learn the machine

Six women became central early programmers: Kay McNulty, Betty Jennings, Betty Snyder, Marlyn Wescoff, Fran Bilas and Ruth Lichterman, later known under several married names. They studied diagrams and worked out how to translate mathematical problems into a sequence the machine could perform. Their task was technical reasoning about the hardware, not simply entering numbers after someone else had completed all the difficult work.

The machine’s intelligence in public depended on instructions worked out away from the spotlight.

4. The demonstration must actually run

Preparing the 1946 unveiling required a problem that would show ENIAC’s speed and flexibility. The programmers had to configure the sequence, understand timing and find errors that could prevent the demonstration from working. A machine advertised as revolutionary could still produce nothing useful if one part of the planned calculation was connected or sequenced incorrectly.

The giant brain needed a carefully arranged set of instructions before it could impress anyone.

5. The public sees electronic speed

In February 1946, ENIAC was introduced publicly with demonstrations that attracted substantial attention. The machine’s rapid calculations made the promise of electronic computing tangible. Reports concentrated on the enormous hardware and its designers, while the programming work received far less recognition. The spectacle encouraged people to see a self-sufficient machine even though its performance depended on the people who prepared it.

The cabinets were photographed more easily than the reasoning that made them useful.

6. The first-computer label needs care

ENIAC was a landmark general-purpose electronic digital computer, but it was not the first calculating machine or the first computer under every possible definition. Other systems, including wartime and electromechanical machines, had their own priority claims. Its original programming also differed from later stored-program designs. Precise descriptions make its contribution clearer than awarding one universal first place to an entire field’s history.

The achievement becomes more interesting when the label stops trying to erase its neighbours.

7. The programmers return to the story

Later historical work helped restore recognition of the six women’s contributions. Their story changes how the unveiling is understood: the celebrated machine was a partnership between electronic engineering, mathematics and programming labour. The computer did not replace the need for skilled thought. It created a new place where that thought could work at electronic speed, provided someone could first explain the problem to the hardware.

The machine was revolutionary. Remembering who programmed it should not have taken another revolution.