A Chronology of Digital Computing Machines (to 1952)

A Chronology...The Jargon FileComputer Dictionary
Jay W. Forrester and his team at MIT construct the "Whirlwind" for the US Navy's Office of Research and Inventions. The vague date is because it advanced to full-time operational status gradually. Originally it had 3300 tubes and 8900 crystal diodes. It occupied 2500 square feet of floor. Its 2048 16-bit words of CRT memory used up tubes so fast they were costing $32000 per month.
This was the first computer designed for real-time work, hence the short word size; it could do 500000 additions or 50000 multiplications per second.
Spring 1949
Forrester conceives the idea of magnetic core memory. The first practical form, 4 years later, will replace the Whirlwind's CRT memory and render all then existing types obsolete.
Jun 1949
Maurice Wilkes (1913-) and his team at Cambridge University complete the "EDSAC" ("Electronic Delay Storage Automatic Computer"), which is closely based on the EDVAC design report from von Neumann's group. This is the first operational stored-program computer that's not a prototype. Its I/O is by paper tape, and it has a sort of mechanical read-only memory for booting, consisting of rotary telephone switches.
Its main memory is of another new type, invented by Eckert: the "ultrasonic" or "delay line" memory. In this type, the data is repeatedly converted back and forth between electrical pulses and ultrasonic pulses; only the bits currently in electrical form are accessible. (The ultrasonic pulses were typically fired from one end of a tank of mercury to the other, though other substances were also used.) In the EDSAC, 32 mercury tanks 5 feet long give a total of 256 35-bit words of memory.
Aug 1949.
Eckert and Mauchly, having formed their own company, complete the "BINAC" ("Binary Automatic Computer") for the US Air Force. Designed as a first step to in-flight computers, this has dual (redundant) processors each with 700 tubes and 512 31-bit words of memory. Each processor occupies only 4 square feet of floor space and can do 3500 additions or 1000 multiplications per second.
The designers are thinking mostly of their forthcoming "UNIVAC" ("Universal Automatic Computer") and don't spend much time making the BINAC as reliable as it should be, but the tandem processors compensate somewhat.
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