A computer is an electronic machine that obeys instructions telling it how to present information in a more useful form. Its HARDWARE is the actual machine, including parts such as the screen. The hardware stores instructions as a computer program, or SOFTWARE. Hardware and software work together to change basic data into something people can use. A long list of numbers, for example, can be presented as a colourful picture.


The body of the computer and the devices that plug into it, such as the keyboard, are called its hardware. The body contains the parts that store and process information. These include the hard disk, which stores programs and files permanently. Faster, electronic memory holds the data being processed. A chip called the processor does most of the work, helped by others that do special jobs, such as displaying images.


Today’s personal computer may have a big colour screen, loudspeakers, and possibly a camera. It is thousands of times more powerful than computers built around 30 years ago, which were so bulky they could fill a whole room. This improvement is due to the microprocessor (invented in 1971), which replaced hundreds of separate computer parts with a single microchip.


A computer’s hard disk (usually several disks spinning together) stores information permanently as magnetic spots on the disks’ surface. The hard disk is too slow to keep up with the processor, so all data has to be read from the disk into fast, electronic RAM (random-access memory) before use. RAM chips stop working as soon as the computer is switched off, so new data needed again must be saved on the hard disk.


Table 6. 

BitSmallest unit of information
Byte Eight bits
Kilobyte 1,024 bytes
Megabyte1,024 kilobytes
Gigabyte 1,024 megabytes

Computers store and process information in the form of bits. A bit can stand for one of just two different things, such as “yes” and “no”. For example, a hard disk stores information as magnetic spots with the magnetism pointing up or down. When bits are grouped together, they allow more choices. Every extra bit doubles the possibilities, so a byte can stand for 256 different things. A modern PC can handle billions of bits per second and store up to 120 gigabytes (over 1,000 trillion bits) on its hard disk.


A computer needs software, which consists of sets of instructions called programs, to tell it what to do. Different programs allow people to write letters, play games, or connect to the Internet. Software is written in special languages by computer programmers. The languages are then translated into instructions that can be understood by the computer’s microprocessor.

Copyright © 2007 Dorling Kindersley


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