The Manchester Baby, the world's first stored program computer, ran its first program

21st June 1948
The Manchester Baby, the world's first stored program computer, ran its first program

On June 21st, 1948, at Manchester University, shortly after 11 o'clock in the morning, the world's first stored-program electronic digital computer successfully executed its first program. That program was written by Tom Kilburn who, along with Freddie Williams designed and built the machine. It was called the Small-Scale Experimental Machine, but was soon nicknamed "The Baby". it is also  known as the "Mark 1 prototype".

Freddie Williams started work in July 1946 on a form of digital storage using a Cathode Ray Tube, at the Telecommunications Research Establishment (TRE) at Malvern. He demonstrated the successful operation of a single bit memory using the "anticipation pulse method" in early October, and provisionally patented this system in December 1946. The bit was stored in the form of a charge on the CRT screen's phosphor, which could be controlled by the electron beam to write a 0 or a 1. Although the phosphor was an electrical insulator, the charge would leak away in the order of a second. Freddie Williams arranged to read the charge and then rewrite it continuously at electronic speeds so that information could be kept permanently; this process was called "regeneration" and the principle is still used today to replenish charge on modern integrated circuit RAMs.

Though the store could remember 2048 bits, an individual bit could only be reset by hand, and it was necessary to test its capability of setting and reading any required bit at electronic speeds and remembering its value indefinitely between settings. So the next step was to build a small computer around a CRT memory, to subject it to the "most effective and searching tests possible". This computer, the Small Scale Experimental Machine, included the stored-program concept, so that the Random Access Memory was used not only to hold numbers involved in calculations, but to hold the program instructions. This meant that instructions could be read successively at electronic speed, and that running a different program only involved resetting part of the memory using a simple keyboard rather than reconfiguring the electronic circuitry (this could take days on ENIAC).

F.C. Williams later said of the first successful run:

"A program was laboriously inserted and the start switch pressed. Immediately the spots on the display tube entered a mad dance. In early trials it was a dance of death leading to no useful result, and what was even worse, without yielding any clue as to what was wrong. But one day it stopped, and there, shining brightly in the expected place, was the expected answer. It was a moment to remember. This was in June 1948, and nothing was ever the same again."

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The Manchester Baby, the world's first stored program computer, ran its first program

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