Byte Order Mark

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Byte Order Mark

A Byte Order Mark (BOM) is a character sequence that specifies the byte order of a text file, indicating whether the data is stored in little-endian or big-endian format. It is typically placed at the beginning of a file to ensure correct interpretation of the file’s contents by applications and systems.

What does Byte Order Mark mean?

In computing, a Byte Order Mark (BOM) is a Character sequence inserted into the beginning of a text file to indicate the byte order of the file, particularly whether it is big-endian or Little-Endian. This is necessary because different computer architectures store data in different ways, and without a BOM, it would be difficult to determine the correct order of the bytes in a file.

BOMs are typically used in text files, such as plain text, XML, and CSV files. They are not required for binary files, as the byte order is determined by the file Format. However, BOMs can still be helpful in binary files to ensure that data is interpreted consistently.

There are three common types of BOMs:

  • UTF-8 BOM: 0xEF 0xBB 0xBF
  • UTF-16 BOM (big-endian): 0xFE 0xFF
  • UTF-16 BOM (little-endian): 0xFF 0xFE

The UTF-8 BOM is the most commonly used, as it is supported by most text editors and applications. The UTF-16 BOMs are only used in Unicode files.

Applications

BOMs are important in technology today because they help to ensure that data is interpreted consistently across different computer architectures. This is especially important for text files, as the byte order of the file can affect the meaning of the text. For example, the following two strings of text are identical in terms of the characters they contain, but they have different meanings depending on the byte order:

AB

BA

If the file is big-endian, the first string represents the number 0x4142, while the second string represents the number 0x4241. If the file is little-endian, the first string represents the number 0x4241, while the second string represents the number 0x4142.

By using a BOM, it is possible to ensure that the byte order of a file is correct, regardless of the Computer Architecture it is running on. This helps to prevent data corruption and other problems.

History

The first BOMs were developed in the early 1990s, as part of the Unicode standard. The UTF-8 BOM was added to the standard in 1996, and the UTF-16 BOMs were added in 1999.

BOMs have become increasingly important over time, as Unicode has become the dominant character encoding for text files. Today, most text editors and applications support BOMs, and they are widely used to ensure that data is interpreted consistently across different platforms.