In most computer systems, a byte is a unit of information that is eight bits long. A byte is the unit most computers use to represent a character such as a letter, number, or typographic symbol (for example, "g", "5", or "?"). A byte can also hold a string of bits that need to be used in some larger unit for application purposes (for example, the stream of bits that constitute a visual image for a program that displays images).

In some computer systems, four bytes constitute a word, a unit that a computer processor can be designed to handle efficiently as it reads and processes each instruction.

Some computer processors can handle two-byte or single-byte instructions. A byte is abbreviated with a "B". (A bit is abbreviated with a small "b".) Computer storage is usually measured in byte multiples (for example, an 820 MB hard drive holds a nominal 820 million bytes (megabytes) of information. (The number is actually somewhat larger since byte multiples are calculated in powers of 2 and we express them as decimal numbers .)

A 28.8 Kbps modem is one that operates at 28.8 thousand bits (kilobits) per second. (Storage is measured in bytes; transmission capacity in bits per second.) Some language scripts require two bytes to represent a character. These are called double-byte character sets (DBCS).