Octet Definition

An octet is eight consecutive bits. It is equivalent to a byte, as long as the byte is also eight bits.

A bit is the most basic unit of information in computing and communications, and it always has a value of either zero or one. A byte is a contiguous sequence of a fixed number of bits that is used as a unit of memory, storage and instructions execution in computers.

The number of bits in a byte varied according to the model of computer and its operating system in the early days of computing. For example, the PDP-7, for which the first version of UNIX was written, had 18-bit bytes. Today, however, a byte virtually always consists of eight bits.

As is the case with an eight-bit byte, an octet can be expressed both as a decimal integer ranging from zero to 255 and as a pair of hexadecimal (i.e., base 16) digits ranging from 00 to FF.

Each of the four number groups that comprise the 32-bit IP addresses used in IPv4, the current mainstream addressing protocol for the Internet, is also an octet. The word quad has the same meaning as octet in this context.

Created December 4, 2005.
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