# 2 The parts of a computer

A computer is a machine that manipulates data following a list of instructions that have been programmed into it. Input devices are used to input data into a computer. Many of the earliest computers read their input from paper tape adapted from existing ticker tape technology. Figure 2 shows such a computer, Colossus 10.

Figure 2 Colossus 10 in Block H of Bletchley Park, now part of The National Museum of Computing.

The large frame on the right of the picture with wheels attached is the input device. It guides paper tape with the stream of characters from an intercepted message punched into it. The tape was read into Colossus at 30 mph. Another existing technology, the electric typewriter, was used as an output device to print out the results from Colossus.

In the years since Colossus and ENIAC, many other technologies have been adapted or created to use as input and output devices. The keyboard of a personal computer, the scanner of a bar-code reading system and the switches or buttons of a microwave oven are some examples of input devices. There are many different types of output device. The actuator that switches on a pump of a computer-controlled central-heating system is one example; the sound system that generates the beep of an electronic heart monitor is another.

Sometimes the two types of device can be the same physical device. The electric typewriter was adapted first as an output device and later an input device. Today the touchscreen is widely used for both input and output.

OpenLearn - An introduction to computers and computer systems
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