Globally Unique Identifier (GUID), GUID is a 128-bit globally unique identifier (GUID), which is composed of a 128-bit binary number (16 bytes) and can be used for all computers and networks that require a unique identifier. The possibility of this identifier being repeated is very small. The format of GUID is "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx", where each x is a hexadecimal number in the range of -9 or a-f.