A creator ID or type ID is a unique 4-character identifier for an organization, product, or file format. Most notably used on the Apple Macintosh to represent individual applications and file types. Creator IDs are similar to stock ticker symbols in both use and form.
Unique 4-character identifiers are common to many sectors in the computer industry. For example, USB devices broadcast their manufacturer's ID and their device ID to the host operating system. The host then uses this information to determine which device driver to map to the device. Palm OS, heavily influenced by Mac OS, also uses creator IDs to determine which application owns what data.
A creator ID contains at most four ASCII characters.
Characters are limited to ASCII 33-127 (decimal). Generally only the space character, a to z, A to Z, and 0 to 9 are used.
Creator IDs must be registered with a central authority (a registry) before commercial use.
Lower-case creator IDs are generally reserved for use by the parent organization of the OS or device class. For example, the Palm OS Address Book application (built by PalmSource) has the creator ID 'addr'.
Creator IDs must be unique between all creator IDs within the OS or device class.
When programming, creator IDs are easily represented as a four character array, which in turn can be represented as a 32-bit integer. Sorting and comparisons are made trivially fast through integer math vs. string comparison.