The Whirlwind computer was developed at the Massachusetts Institute of Technology. It is the first computer that operated in real time, used video displays for output, and the first that was not simply an electronic replacement of older mechanical systems. Its development led directly to the US Air Force's SAGE system, and indirectly to almost all business computers in the 1960s.

History

During World War II the US Navy approached MIT about the possibility of creating a computer to drive a flight simulator for training bomber crews. They envisioned a fairly simple system in which the computer would continually update a simulated instrument panel based on control inputs from the pilots. Unlike older systems like the Link Trainer, the system they envisioned would have a considerably more realistic aerodynamics model that could be adapted to any type of plane.

A short study by the MIT Servomechanisms Laboratory concluded that such a system was certainly possible. The Navy decided to fund development under Project Whirlwind, and the lab placed Jay Forrester in charge of the project. They soon built a large analog computer for the task, but found that it was inaccurate and inflexible. Solving these problems would require a much larger system, perhaps one so large as to be impossible to construct.

In 1945 Jerry Crawford, another member of the MIT team, saw a demonstration of ENIAC and suggested that a digital computer was the solution. Such a machine would allow the accuracy of the simulation to be improved with the addition of more code in the computer program, as opposed to adding parts to the machine. As long as the machine was fast enough, there was no theoretical limit to the complexity of the simulation.

Up until this point all computers constructed were dedicated to single tasks, run in batch mode. A series of inputs were set up in advance and fed into the computer, which would work out the answers and print them. This was not appropriate for the Whirlwind system, which needed to operate continually on an ever-changing series of inputs. Speed became a major issue, whereas with other systems it simply meant waiting longer for the printout, with Whirlwind it meant seriously limiting the amount of complexity the simulation could include.

By 1947, Forrester and Everett completed the design of a high-speed stored-program computer for this task. Construction started the next year, an effort that employed 175 people including 70 engineers and technicians. Whirlwind took 3 years to build and first went online on April 20th, 1951. By that point the Navy had already lost interest in Project Whirlwind, but development had been picked up by the Air Force under Project Claude.

Speed of the original design (20 KIPS) turned out to be too slow to be very useful, and most of the problem was attributed to the fairly slow speed of the Williams tubes used for main memory. Forrester started looking at replacements, first using magnetic tape formed into spirals, and eventually creating core memory. Speed was roughly doubled (40 KIPS) as a result of using core when the new version was completed in 1953.

The new core-based machine was fast enough for use in SAGE, and an industrial effort was started in order to mass-produce the machines for this role. RCA was a front-runner, but IBM was eventually selected instead. They started production in 1957, along with a massive construction project to build the buildings, power and communications network needed to feed the SAGE systems with data.

An effort was also started to convert the Whirlwind design to a transistorized form, led by Kenneth Olsen and known as the TX-0. TX-0 was very successful and plans were made to make an even larger version known as TX-1. However this project was far too ambitious and had to be scaled back to a smaller version known as TX-2. Even this version proved troublesome, and Olsen left in mid-project to start DEC.

Further Reading

• John F. Jacobs, The SAGE Air Defense System: A Personal History (MITRE Corporation, 1986) also contains much material on the Whirlwind

External link

• Computer Structures: Readings & Examples — The Whirlwind I computer (http://www.research.microsoft.com/~gbell/Computer_Structures__Readings_and_Examples/00000157.htm)
• Whirlwind documentation (http://www.bitsavers.org/pdf/mit/whirlwind)