A calculator is generally defined as (1) any small handheld device that automatically performs arithmetic operations, certain mathematical functions, simple text editing, or elementary programming, or (2) a software program on a computer that simulates a "real" handheld calculator; for example, both Apple's Mac OS and Microsoft's Windows operating systems contain a simple desktop calculator program that allows a computer user to perform simple mathematical calculations.

While the calculator is a relatively modern invention, various simple calculating machines able to perform addition and subtraction have existed for centuries. The abacus, a memory-helping device rather than a true calculating device, is an instrument for carrying out simple arithmetic operations. It was possibly first used around 3000 B.C. in Babylonia. This device allowed users to make computations using a system of sliding beads arranged on a rack. The first attempt to design a calculating machine was probably made by Leonardo da Vinci...