A machine that can be programmed to manipulate symbols. Computers can perform complex and repetitive procedures quickly, precisely and reliably and can quickly store and retrieve large amounts of data.
The physical components from which a computer is constructed (electronic circuits and input/output devices) are known as "hardware". Most computers have four types of hardware component: CPU, input, output and memory. The CPU (central processing unit) executes programs ("software") which tell the computer what to do. Input and output (I/O) devices allow the computer to communicate with the user and the outside world. There are several kinds of memory - fast, expensive, short term memory (e.g. RAM) to hold intermediate results, and slower, cheaper, long-term memory (e.g. magnetic disk and magnetic tape) to hold programs and data between jobs.
See also analogue computer.