Byte Order Mark

Definition of Byte Order Mark

The Byte Order Mark (BOM) is a Unicode character used at the beginning of a text stream to indicate the byte order, or endianness, of the text encoding. It assists in the interpretation of Unicode text files by specifying whether the data is stored using big-endian or little-endian byte order. BOM serves as a guide for software or text editors, ensuring accurate rendering and processing of Unicode encoded text.


The phonetics for the keyword “Byte Order Mark” would be:B – /baɪt/Y – /waɪ/T – /ti:/E – /i:/O – /oʊ/R – /ɑːr/D – /di:/E – /i:/R – /ɑːr/M – /ɛm/A – /eɪ/R – /ɑːr/K – /keɪ/

Key Takeaways

  1. Byte Order Mark (BOM) is a Unicode character used to signal the endianness (Byte order) of a text file or stream.
  2. BOM assists in the proper rendering and interpretation of Unicode text by indicating the byte order of the characters.
  3. While BOM can be useful in certain situations, it may cause issues in applications not designed to handle it, leading to compatibility problems.

Importance of Byte Order Mark

The Byte Order Mark (BOM) is an important technology term because it signifies the endian order or byte sequence of text data stored in a file, ensuring the proper encoding and decoding of the data when being read, manipulated, or saved.

It is especially crucial when dealing with Unicode-encoded data in various formats such as UTF-8, UTF-16 or UTF-32.

The BOM allows software or applications to correctly identify the encoding method and byte order, preventing data corruption, misinterpretation, and enabling seamless interchange between systems with different byte orders.

In essence, the BOM plays a pivotal role in maintaining data integrity and promoting cross-platform compatibility in the digital world.


The Byte Order Mark (BOM) serves a crucial role in ensuring the proper interpretation of text files, specifically those encoded in Unicode. It deals with the issue of byte order, which refers to the arrangement of bytes in multi-byte number representations, like 16-bit or 32-bit integers. Since computers have varying ways of storing multi-byte numerical values, such as little-endian or big-endian formats, the BOM provides a standardized method to signal the correct order for interpreting these sequences.

By appending a BOM at the beginning of a text file, it helps software, like text editors or parsers, to accurately identify the correct encoding and avoid potential errors or misrepresentations of the textual information. The byte order mark is particularly vital when handling various Unicode encodings, such as UTF-8, UTF-16, and UTF-32. For instance, the BOM in a UTF-16 encoded file allows the software to identify whether the file is using little-endian or big-endian byte ordering.

This is crucial as reading the file using an incorrect byte order may lead to a garbled text display. While the BOM is not required for UTF-8 encoded files, including it ensures compatibility with systems that specifically look for a BOM to determine a file’s encoding. Thus, the BOM provides a valuable solution for maintaining the integrity and accuracy of textual data across diverse systems and software, promoting seamless communication and data interchange in our technologically interconnected world.

Examples of Byte Order Mark

Software Development: Programmers often use various text editors or Integrated Development Environments (IDEs) to create and modify source code. When a source code file is written in a Unicode format, a BOM is added to indicate the endianness (byte order) of that file. The presence of a BOM allows text editors and IDEs to correctly interpret and display the code, especially when non-ASCII characters such as accented letters or characters from non-Latin scripts are present in the file.

Web Development: When serving web pages, the HTTP response encoding should match the actual encoding of the HTML document. If an HTML document contains a BOM, web browsers can use this information to automatically determine the correct encoding (e.g., UTF-8, UTF-16) to properly render the text. This is particularly useful when a web page contains special characters, such as non-Latin scripts, mathematical symbols, or emojis.

Data Interchange: In the context of exchanging data between systems, applications, or platforms, a BOM can help ensure proper interpretation and processing of text files. For example, when importing a CSV file into spreadsheet software or transferring an XML document between different systems, the presence of a BOM can assist those applications or systems to correctly recognize and parse the text data with appropriate encoding.

Byte Order Mark FAQ

What is Byte Order Mark (BOM)?

The Byte Order Mark (BOM) is a Unicode character used to indicate the byte order of a text document. It is especially useful for identifying the order of bytes when handling UTF-encoded text files, allowing the proper interpretation of the content.

Why is the BOM necessary?

Using the BOM is not always required, but it can be helpful when dealing with Unicode-encoded text files, particularly UTF-16 and UTF-32. It provides a clear indication of the byte order used in the file, ensuring that it is read and interpreted correctly by software.

Does the BOM affect ASCII-compatible character encodings?

No, the BOM is specifically designed for Unicode encodings. ASCII-compatible character encodings, such as ISO-8859-1 or Windows-1252, do not require a BOM.

How is the BOM represented in different Unicode encodings?

In UTF-16, the BOM is represented as either the character U+FEFF or U+FFFE, depending on the byte order used (big endian or little endian). In UTF-8, the BOM is represented using the byte sequence EF BB BF. In UTF-32, the BOM appears as the 4-byte sequence 00 00 FE FF for big endian or FF FE 00 00 for little endian.

Can the BOM cause issues with certain text editors?

Some older text editors or software might not recognize the BOM properly, leading to display issues or text corruption when opening a Unicode-encoded file containing a BOM. Most modern software, however, can properly handle BOMs and correctly interpret Unicode files.

Related Technology Terms

  • Encoding Detection
  • Unicode Character Set
  • UTF-8, UTF-16, UTF-32
  • Endianess
  • Text File Signature

Sources for More Information


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