binary file

A computer file format in which each character position can hold any one of 256 different binary codes. Binary files are contrasted to "ASCII files," which contain a smaller set of codes for only alphabetic letters, numeric digits, special symbols and a few control codes. Binary files can contain ASCII and many more codes because they use all eight bits of the byte, whereas ASCII files use only seven bits, which limits the possible combinations.

Executable software (machine language programs), most word processing files and database, spreadsheet and multimedia files are binary files. However, text and source program files as well as HTML and XML files are ASCII text files, not binary.

Attachments Must Be Encoded
The binary vs. ASCII distinction is made when attaching files via e-mail. The Internet's SMTP mail protocol supports only ASCII. When binary files are attached to e-mail messages, their 8-bit format is converted into a temporary 7-bit format to pass through mail servers, especially older ones. Encoding formats such as MIME, UUcoding and BinHex are used, and at the receiving end, they convert the 7-bit code back into 8-bit binary files. The 8-bit to 7-bit conversion makes attached files larger as they traverse the Internet. See binary, byte and ASCII.

binary file [′bīn·ə·rē ′fīl]

(computer science)

A computer program in machine language that can be directly executed by the computer.

(file format)

binary file - Any file format for digital data that does not consist of a sequence of printable characters (text). The term is often used for executable machine code.

All digital data, including characters, is actually binary data (unless it uses some (rare) system with more than two discrete levels) but the distinction between binary and text is well established. On modern operating systems a text file is simply a binary file that happens to contain only printable characters, but some older systems distinguish the two file types, requiring programs to handle them differently.

A common class of binary files is programs in machine language ("executable files") ready to load into memory and execute. Binary files may also be used to store data output by a program, and intended to be read by that or another program but not by humans. Binary files are more efficient for this purpose because the data (e.g. numerical data) does not need to be converted between the binary form used by the CPU and a printable (ASCII) representation. The disadvantage is that it is usually necessary to write special purpose programs to manipulate such files since most general purpose utilities operate on text files. There is also a problem sharing binary numerical data between processors with different endianness.

Some communications protocols handle only text files, e.g. most electronic mail systems before MIME became widespread in about 1995. The FTP utility must be put into "binary" mode in order to copy a binary file since in its default "ascii" mode translates between the different newline characters used on the sending and receiving computers.

Confusingly, some word processor files, and rich text files, are actually binary files because they contain non-printable characters and require special programs to view, edit and print them.