Binary digits. Artwork depicting a stream of binary digits on a surface. Binary numbers belong to a base-two counting system. The binary notation uses just two digits, '0' and '1'. This lends itself easily to computing, where the digits may be represented by switches having two states, 'on' and 'off'. Despite its high-tech image, the binary system may be derived from 'two-counting', probably the most ancient system in the history of mathematics.