Abacus

The abacus (plural abaci or abacuses), also called a counting frame, is a calculating tool that has been in use since ancient times and is still in use today. It was used in the ancient Near East, Europe, China, and Russia, centuries before the adoption of the written Arabic numeral system. The exact origin of the abacus is unknown. The abacus essentially consists of a number of rows of movable beads or other objects, which represent digits. One of two numbers is set up, and the beads are manipulated to implement an operation involving a second number (e.g., addition), or rarely a square or cubic root.

In earliest use the rows of beads could be loose on a flat surface, or sliding in grooves. Later the beads were made to slide on rods of some sort built into a frame, allowing faster manipulation. Abacuses are still made, often as a bamboo frame with beads sliding on wires. In the ancient world, particularly before the introduction of positional notation, abacuses were a practical calculating tool.

There are distinctive modern implementations of the abacus. Some designs, like the bead frame consisting of beads divided into tens, are used mainly to teach arithmetic, although they remain popular in the post-Soviet states as a tool. Other designs, such as the Japanese soroban, have been used for practical calculations even involving numbers of several digits. For any particular abacus design, there are usually numerous different methods to perform calculations, which may include the four basic operations, and also square and cube roots. Some of these methods work with non-natural numbers (numbers such as 1.5 and ​3⁄4).

Although today calculators and computers are usually used instead of abacuses, abacuses still remain in common use in some countries. Merchants, traders and clerks in some parts of Eastern Europe, Russia, China and Africa use abacuses, and they are still used to teach arithmetic to children. Some people who are unable to use a calculator because of visual impairment may use an abacus.