Byte order mark facts for kids
A Byte Order Mark (BOM) is like a secret code at the very beginning of a text file. It tells computers how the text inside the file is organized, especially when it uses a special way of writing characters called Unicode. Think of it as a tiny label that helps computers understand the language of the file.
The actual code for a BOM is `U+FEFF`. This code looks a bit different depending on the specific Unicode encoding used.
| Bytes (Computer Code) | Encoding Type |
|---|---|
| EF BB BF | UTF-8 |
| FE FF | UTF-16, big-endian |
| FF FE | UTF-16, little-endian |
| 00 00 FE FF | UTF-32, big-endian |
| FF FE 00 00 | UTF-32, little-endian |
Using a BOM is optional, meaning it's not always needed. But if a file has one, it must be right at the very start. The BOM helps the computer know if the text is in UTF-8 or UTF-16. For UTF-16 and UTF-32, it also tells the computer about something called endianness. This is important when files move between different computer systems that store information in slightly different ways.
What is Endianness?
Endianness describes the order in which a computer stores groups of bytes (pieces of data).
- Big-endian means the most important byte (the "biggest" part) comes first.
- Little-endian means the least important byte (the "smallest" part) comes first.
It's like writing a date: some countries write day-month-year (little-endian for the year), while others write year-month-day (big-endian for the year). The BOM helps computers know which order to expect.
UTF-8 and the BOM
Today, UTF-8 is the most common way to encode text. Because of this, the `EFBBBF` BOM (often called the UTF-8 signature) is seen most often. Web browsers like those you use to surf the internet are designed to recognize this UTF-8 BOM. When they see it, they know how to correctly display the text on a webpage.
The official Unicode rules don't actually require or strongly suggest using a BOM for UTF-8. However, they do warn that you might find it at the beginning of a file.
When BOMs Can Cause Trouble
Most modern computer programs can easily understand and use a BOM. They might even add one automatically when you save a text file. However, sometimes the UTF-8 BOM can cause problems. This usually happens with older software that wasn't made to handle UTF-8. In these cases, the BOM might show up as strange characters like "" at the start of your text.
See also
In Spanish: Marca de orden de bytes para niños
