What is an abacus, and how long has it been used?

An abacus, also called a counting frame, is a calculating tool used for mathematical problems. Abaci are often constructed as a wooden frame with beads sliding on wires, but originally they were beans or stones moved in grooves in sand or on tablets of wood, stone, or metal. These early abaci were documented in Mesopotamia around 3500 B.C.E. The modern form, with beads sliding on rods, dates back to at least fifteenth-century China. Before the use of decimal number systems, which allowed the familiar pencil-and-paper methods of calculation, the abacus was used for almost all multiplication and division. The abacus is still used in many countries where modern calculators are not available. It is also widely used in Japan and China, both of which have long traditions of abacus use.

The abacus can be thought of as an old-fashioned adding machine. It uses beads to represent numbers that can be added and subtracted by moving them back and forth along columns.