"We spent the better part of $1 million figuring out what was going on," he recalls. "There were probably 50 variables," including which elements to use, how finely to grind them, at what temperature to fire them and for how long. By 1952, Forrester's lab had perfected the material that made magnetic-core memory viable. The result, Forrester says, was memory that "was completely reliable and relatively inexpensive."

The development of Whirlwind itself ultimately eclipsed the flight-simulator project. Forrester's team had stopped working on the simulator in June 1948, and navy support for Whirlwind waned. "We probably would've been pretty well budgeted out of existence, except for Russia exploding the atomic bomb" in 1949, says Forrester. "That brought into sharp relief the weakness--or almost nonexistence--of the American air defense system." The air force stepped in to fund Whirlwind, and Forrester led the division at MIT's Lincoln Lab that designed the Whirlwind-based SAGE air defense system, which operated until 1983.

Whirlwind's greatest legacy, however, was magnetic-core memory, which Forrester says made the first two-plus decades of digital computing possible. "We spent about seven years trying to convince the industry that it was a good idea," he says. "Then we spent about seven years in patent courts trying to convince them that they hadn't all thought of it first."