While working on Project Whirlwind at MIT, Forrester invented random-access, coincident-current magnetic storage, which became the standard for digital computers, replacing electrostatic tubes. It was the first reliable, high-speed random access memory for digital computers. The patent was granted in 1956.
The 3D magnetic structure consisted of many stacked planes. The planes were made of wires and magnetic rings called cores, each containing a bit of data. The hand-wired planes held about 4000 cores, and the bits could be accessed with a single read-and-write cycle.
Information could be requested and received from memory in a microsecond, which is hundreds of thousands of times slower than memory today, but was unheard of speed at the time. This method of storage was used in computers into the 1970s.
Project Whirlwind started at the MIT Servomechanisms Laboratory in 1944, focusing on developing a flight simulator using an analog computer, but it would become one of the first large-scale, high-speed digital computers. The project became the Digital Computer Laboratory at MIT, which Forrester directed.
Whirlwind I was completed in 1951 and it was the first electronic, stored-program digital computer to operate in real-time. It led to Whirlwind II, which was the basis for the US air defense system SAGE and many other computers.
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