Video Display Terminal Manchester Computer  Inventors of the Modern Computer Series • Table of Contents • Next Chapter John Bardeen, Walter Brattain and William Shockley - The Transistor ENTER

More on Mark 1 Computer - Williams Tube - Frederick Williams and Tom Kilburn • Further Reading: Biographies of Frederick Williams and Tom Kilburn. How the Williams-Kilburn Tube operated. Tom Kilburn's original notes for the world's first stored computer program. Pictures of the Manchester Mark 1 and the Ferranti Mark 1.

By 1946, a winner in the data-storage game emerged that would dominate the computer field for the next several years. Sir Frederick Williams and Tom Kilburn co-invented the Williams-Kilburn Tube (or Williams Tube), a type of altered cathode-ray tube. Scientists had conducted research on cathode-ray tubes serving as computer data storage since the early 1940s.

The illustration to the right is an example of the video display terminal used with the Manchester computer. The terminal mirrored what was happening within the Williams Tube. A metal detector plate placed close to the surface of the tube, detected changes in electrical discharges. Since the metal plate would obscure a clear view of the tube, the technicians could monitor the tubes used a video screen. Each dot on the screen represented a dot on the tube's surface; the dots on the tube's surface worked as capacitors that were either charged and bright or uncharged and dark. The information translated into binary code (0,1 or dark, bright) became a way to program the computer.

The Williams Tube provided the first large amount of random access memory (RAM), and it was a convenient method of data-storage. It did not require rewiring each time the data was changed, and programming the computer went much faster. It became the dominant form of computer memory until outdated by core memory in 1955.

History of the Manchester Baby
In December 1946, Williams began to chair the Department of Electrical Engineering at the University in Manchester, England, with Tom Kilburn moving to Manchester as well. The men had both worked for the Telecommunications Research Establishment (TRE) in Malvern, England, trying to improve the digital storage ability of a cathode-ray tube.

Williams had already succeeded in storing one bit of information on a cathode-ray tube and had filed a provisional patent in December of 1946. Tom Kilburn soon devised an improved method of storing bits, increasing the storage capacity to 2048 bits. Williams added Kilburn's name to the patent. The team was ready to build a computer based on the Williams Tube.

In 1948, Tom Kilburn, assisted by another TRE researcher, Geoff Tootill, worked on designing and building a prototype machine. Nicknamed "The Baby," the new computer demonstrated the ability of the Williams Tube. For the first time in history, a computer used a stored program. Tom Kilburn wrote that computer program, first executed on June 21, 1948.
 

Manchester Baby's Specifications

32-bit word length.

Serial binary arithmetic using 2 complement integers.

Single address format order code.

Random access main store of 32 words, extendable up to 8192 words.

Computing speed of around 1.2 milliseconds per instruction.

The team designed a second computer (Manchester Mark 1) and commissioned an outside company called Ferranti Ltd. to build the computer in 1949. Ferranti Ltd. and the Manchester University team collaborated in 1951 and built the world's first commercially available general-purpose computer called the Ferranti Mark 1. The first machine off the production line was delivered to the University of Manchester.
 

Manchester Mark 1 Specs - Ferranti Mark 1 Specs

Store organized in 40-bit addressable "lines," holding one 40-bit number or two 20-bit instructions.	Store organized in 20-bit addressable "lines," an instruction taking one line and a number two consecutive lines.
Serial 40-bit arithmetic with hardware add, subtract, and multiply and logical instructions.	Serial 40-bit arithmetic, with hardware add, subtract, and multiply and logical instructions and simple B-line arithmetic.
2 modifier registers (B-lines, for modifying addresses in instructions.)	8 modifier registers (B-lines, for modifying addresses in instructions.)
Single address format order code - about 30 function codes.	Single address format order code - about 50-function codes.
4 pages of random access main store.	8 pages of random access main store.
128-page capacity drum backing store, 2 pages per track, about 30 milliseconds revolution time.	512-page capacity drum backing store, 2 pages per track, about 30 milliseconds revolution time.
Standard instruction time - 1.8 milliseconds, multiplication much slower.	Standard instruction time - 1.2 milliseconds, multiplication 2.16 milliseconds.
Peripheral Instructions: read and punch a line of 5 hole paper tape; transfer a given page or track on drum to/from a given Williams Tube "page" or page pair in store.	Peripheral Instructions: read and punch a line of 5 hole paper tape; transfer a given page or track on drum to/from a given Williams Tube "page" or page pair in store.

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artwork©marybellis 
original photos©"army photos"