10.1 Globally Unique Identifiers (GUIDs)

A GUID is the Microsoft implementation of a universally unique identifier. A GUID is a 128-bit value consisting of one group of 8 hexadecimal digits, followed by three groups of 4 hexadecimal digits each, and followed by one group of 12 hexadecimal digits, for example {6B29FC40-CA47-1067-B31D-00DD010662DA}, (see Table 38).

Table 38 GUID Structure

Field NameOffset(byte)Size(bytes)Comments
Data104This field is mandatory and contains the four bytes from the first group of the GUID (6B29FC40h from the example).
Data242This field is mandatory and contains the two bytes from the second group of the GUID (CA47h from the example).
Data362This field is mandatory and contains the two bytes from the third group of the GUID (1067h from the example).
Data4[0]81This field is mandatory and contains the most significant byte from fourth group of the GUID (B3h from the example).
Data4[1]91This field is mandatory and contains the least significant byte from the fourth group of the GUID (1Dh from the example).
Data4[2]101This field is mandatory and contains the first byte from the fifth group of the GUID (00h from the example).
Data4[3]111This field is mandatory and contains the second byte from the fifth group of the GUID (DDh from the example).
Data4[4]121This field is mandatory and contains the third byte from the fifth group of the GUID (01h from the example).
Data4[5]131This field is mandatory and contains the fourth byte from the fifth group of the GUID (06h from the example).
Data4[6]141This field is mandatory and contains the fifth byte from the fifth group of the GUID (62h from the example).
Data4[7]151This field is mandatory and contains the sixth byte from the fifth group of the GUID (DAh from the example).

10.2 Partition Tables

To ensure interoperability of exFAT volumes in a broad set of usage scenarios, implementations should use partition type 07h for MBR partitioned storage and partition GUID {EBD0A0A2-B9E5-4433-87C0-68B6B72699C7} for GPT partitioned storage.