Monday, January 23, 2006

A: The distinction is subtle, but important. The term _byte_ refers to a computer-dependent character size, while _octet_ always means 8 bits (independent of the computer). I have worked on several computers that had odd byte sizes. For example, Purdue once had a CDC mainframe with 6-bit bytes, and I also used a BBN computer (the C machine) on which a byte contained 10 bits.

In practice, most computers have 8-bit bytes and most engineers and programmers mean ``an 8-bit quantity'' when they use the term _byte_. In a texbook, however, which can be read by people with various backgrounds and who use various computers, it is important to make the distinction

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There has been some disagreement, and even controversy, surrounding the use of the words byte and octet. The former term has traditionally been the most popular in common parlance for a set of eight bits, especially in North America. However, it is technically not the correct term.

A byte is, formally, the smallest unit of data that can be read from or written to at one time in a computer system. In almost all cases today, that is indeed eight bits, but there are have been some systems where a byte was not eight bits. Some older 36-bit computers used 9-bit bytes, and there were also systems that had byte sizes of 6 or 7 bits, or even variable-sized bytes. For this reason, many people, especially techie professionals, prefer the term octet, which clearly and unambiguously implies “eight”. This term is much more common outside North America.

This matter of octets and bytes is another of the little “tempests in tea pots” that computer people seem to love so much. The bottom line in modern computer systems, however, is that an octet is a byte and a byte in an octet, and the terms can be used interchangeably without too much danger. You will more often see octets used in technical standards. In this Guide, I use the term bytes for a simple reason: it is the term that most people are familiar with, including myself (though bear in mind that I live in North America; if I were European I might have rather different views on this!)

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