The Computer A machine that performs tasks, such as mathematical calculations or electronic communication, under the control of a set of instructions called a program is a computer. Programs usually reside within the computer and are retrieved and processed by the computer's electronics, and the program results are stored or routed to output devices, such as video display monitors or printers. Computers are used to perform a wide variety of activities with reliability, accuracy, and speed. People use computers in a wide variety of ways. In business, computers track inventories with bar codes and scanners, check the credit status of customers, and tran