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In computing, a single binary digit, either 0 or 1. A bit is the smallest unit of data stored in a computer; all other data must be coded into a pattern of individual bits. A byte represents sufficient computer memory to store a single character of data, and usually contains eight bits. For example, in the ASCII code system used by most microcomputers the capital letter A would be stored in a single byte of memory as the bit pattern 01000001.

The maximum number of bits that a computer can normally process at once is called a word. Microcomputers are often described according to how many bits of information they can handle at once. For instance, the first microprocessor, the Intel 4004 (launched in 1971), was a 4-bit device. In the 1970s several different 8-bit computers, many based on the Zilog Z80 or Rockwell 6502 processors, came into common use. In 1981, the IBM Personal Computer (PC) was introduced, using the Intel 8088 processor, which combined a 16-bit processor with an 8-bit data bus. Business micros of the later 1980s began to use 32-bit processors such as the Intel 80386 and Motorola 68030. Machines based on the first 64-bit microprocessor appeared in 1993.

The higher the number of bits a computer can process simultaneously, the more powerful the computer is said to be. However, other factors influence the overall speed of a computer system, such as the clock rate of the processor and the amount of RAM available. Tasks that require a high processing speed include sorting a database or doing long, complex calculations in spreadsheets. A system running slowly with a graphical user interface may benefit more from the addition of extra RAM than from a faster processor.

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