Elliott 803 - An Early Computer

Elliott 803 Console

Here are some images on an Elliott 803, an early British computer. This is the console through which you could control the computer, load programs or edit memory. One unique feature was a loudspeaker connected to a bit in the currently executing instruction - thus every program that was running had a characteristic ‘tune’ that accompanied it. This allowed the experienced ear to tell when a program was about to fail, and, of course, it allowed enterprising programmers to produce some of the first computer generated music.

The console could be used to change locations in memory or to enter simple programs. The Elliott 803 had a word length of 40 bits, one of which was a parity bit leaving an odd number of bits for actual instructions and data! Each word however could store two instructions (6 bit op-code, 13 bit address) and between them was the B-modifier bit that allowed one instruction to modify how the other instruction behaved.

You can see the Elliott 803 and many other early computers at the National Computer Museum in England.

Elliott 803 Tape Reader

Software was loaded into the Elliott 803 using paper tapes. It had a main memory of 4k or 8k words in one or two blocks of magnetic core store. You could actually see where each bit was stored! Each bit had its own ferrite bead with wires passing through it in both directions. Amazingly you could turn the computer off and back on and wouldn’t have to reload your program into RAM. 30 years later we are finally getting back to technology that can do that with modern SSD drives.

Paper tapes were prepared using a teleprinter. A single typing mistake could mean you would have to copy the entire tape again up to the mistake and then correct the mistake and then carry on copying it. Most people wrote their programs on paper first and then transcribed them to tape. To view the output from running your program you would take the tape that was output by the Elliott 803 and then run it back through a teleprinter. Some users learned how to read paper tapes without a teleprinter and the more advanced user could edit paper tape without a teleprinter using either a single-hole punch or a piece of tape and a chad to fill in a hole. Of course this only worked for in-place, single character edits. Later, teleprinters were connected directly to the computer so it could output without the intermediary paper tape, and thus the interactive session was born and thus interactive games became possible. A Calcomp plotter also allowed the Elliott 803 to draw graphs, and play more sophisticated games like Tank Battle and Lunar lander.

803 Cabinet

The computer itself was huge by modern standards. It required an entire room to house the many cabinets.

Elliott 803 Boards with Minilog devices

The Elliott 803 was created long before integrated circuits existed but they did contain a precursor to the modern IC in the form of Minilog devices. You can see some of them on the board in this shot. Each was a rectangular block with a hard white plastic outer. Inside was a small circuit consisting of a couple of germanium transistors set in resin. A single Minilog might implement a single flip-flop device whereas todays integrated circuits contain billions of flip-flops in a much smaller space.

All pictures courtesy of Peter Onion.

Sat Mar 06 2010 18:42:40 GMT-0800 (Pacific Standard Time)

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