For: byte (disambiguation) A byte ( ) is a basic unit of measurement of information storage in computer science. In many computer architectures it is a unit of memory addressing. There is no standard but a byte most often consists of eight bits.

A byte is an ordered collection of bits, with each bit denoting a single binary value of 1 or 0. The byte most often consists of 8 bits in modern systems; however, the size of a byte can vary and is generally determined by the underlying computer operating system or hardware. Historically, byte size was determined by the number of bits required to represent a single character from a Western character set. Its size was generally determined by the number of possible characters in the supported character set and was chosen to be a divisor of the computer's word size. Historically bytes have ranged from five to twelve bits.

The popularity of IBM's System/360 architecture starting in the 1960s and the explosion of microcomputers based on 8-bit microprocessors in the 1980s has made eight bits by far the most common size for a byte. The term octet is widely used as a more precise synonym where ambiguity is undesirable (for example, in protocol definitions).

There has been considerable confusion about the meanings of SI (or metric) prefixes used with the word "byte", especially concerning prefixes such as kilo- (k or K) and mega- (M) as shown in the chart Prefixes for bit and byte. Since computer memory is designed with dual logic, multiples are expressed in power of two, rather than 10, the software and computer industries often use binary estimates of the SI-prefixed quantities, while producers of computer storage devices prefer the SI values. This is the reason for specifying computer hard drive capacities of, say, "100 GB" when it contains 93 GiB (or 93 GB in traditional units) of addressable storage. Because of the confusion, a contract specifying a quantity of bytes must define what the prefixes mean in terms of the contract (i.e., the alternative binary equivalents or the actual decimal values, or a binary estimate based on the actual values).

Usage

A byte often designates a contiguous sequence of a fixed number of bits (binary digits). The use of a byte to mean 8 bits has become nearly ubiquitous.

When used to describe hardware aspects of a binary computer, it is a contiguous sequence of bits that comprises the smallest addressable sub-field of the computer's natural wordsize. That is, the smallest unit of binary data on which meaningful computation can be applied. For example, the CDC 6000 series scientific mainframes divided their 60-bit floating-point words into 10 six-bit bytes. These bytes conveniently held character data from punched Hollerith cards, typically the upper-case alphabet and decimal digits. CDC also often referred to 12-bit quantities as bytes, each holding two 6-bit display code characters, due to the 12-bit I/O architecture of the machine. The PDP-10 used assembly instructions LDB and DPB to load and deposit bytes of any width from 1 to 36 bits — these operations survive today in Common Lisp. Bytes of six, seven, or nine bits were used on some computers, for example within the 36-bit word of the PDP-10. The UNIVAC 1100/2200 series computers (now Unisys) addressed in both 6-bit (Fieldata) and 9-bit (ASCII) modes within its 36-bit word.