Byte Order Mark

What Does Byte Order Mark Mean?

The byte order mark (BOM) is a piece of information used to signify that a text file employs Unicode encoding, while also communicating the text stream’s endianness. The BOM is not interpreted as a logical part of the text stream itself, but is rather an invisible indicator at its head. The byte order mark’s Unicode character is U+FEFF.


Techopedia Explains Byte Order Mark

Unicode is a group of standards developed in the 1980s and ’90s in order to integrate all of the major computer languages into one coding lexicon. Unicode comes in several iterations, including UTF-8, UTF-16 and UTF-32 (which use 8, 16 and 32 bits per character, respectively).

Before UTF-8 was introduced in 1993, Unicode text was transferred using 16-bit code units. These units had a quality called endianness, which essentially identified the byte order either by least significant first or most significant first. The byte order mark is generally an optional feature in typical, closed-environment text-processing, however it is needed in situations involving text interchange.


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Margaret Rouse is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical, business audience. Over the past twenty years her explanations have appeared on TechTarget websites and she's been cited as an authority in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine and Discovery Magazine.Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages. If you have a suggestion for a new definition or how to improve a technical explanation, please email Margaret or contact her…