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One tonne 'Baby' marks its birth
By Jonathan Fildes
Science and technology reporter, BBC News

Sixty years ago the "modern computer" was born in a lab in Manchester.

The Small Scale Experimental Machine, or "Baby", was the first to contain memory which could store a program.

The room-sized computer's ability to carry out different tasks - without having to be rebuilt - has led some to describe it as the "first modern PC".

Using just 128 bytes of memory, it successfully ran its first set of instructions - to determine the highest factor of a number - on 21 June 1948.

"We were extremely excited," Geoff Tootill, one of the builders of Baby told BBC News.

"We congratulated each other and then went and had lunch in the canteen."

Mr Tootill, and three other surviving members of the Baby team, will be honoured by the University and the British Computer Society at a ceremony in Manchester.

Baby was the successor to machines such as the American ENIAC and the UK's Colossus.

How the BBC reported on the birth of "Baby" in 1948

ENIAC was built to calculate the trajectory of shells for the US army, whilst Colossus was used to decrypt messages from the German High Command during World War II.

Both computers were able to be reprogrammed but this could involve days of rewiring. Baby was designed to overcome this limitation.

"It was the earliest machine that was a computer, in the sense of what everyone today understands a computer to be," explained Chris Burton of the Computer Conservation Society (CCS).

"It was a single piece of hardware which could perform any application depending on what program you put in."

The key to this ability was its memory, built from a cathode ray tube (CRT), which could be used to store a program.

"It was an extraordinary analogue for today's DRAM (dynamic random access memory)," said Mr Burton.

Electrical charges on the screen of the CRT were used to represent binary information. A positive charge represented a one and a negative charge a zero.

A metal grid attached to the screen read the different charges. A graphical representation - dashes for a one and dots for a zero - was displayed on a second CRT wired in parallel to the memory device.

"The operator peered at the monitor tube and he could see the same patterns as in the storage tube," said Mr Burton.

The memory gave programmers a total of 1024 bits, or 128 bytes, to play with. This had to store both the program and all of the data to be crunched.

By comparison, a modern 1GB DRAM chip can store around 8 billion bits.