System — UUID

System — UUID

A UUID is an identifier that is designed to be unique across both time and space, and requires no central registration

process. The UUID is 128 bits long. Its format is described in RFC 4122, but the actual field contents are opaque

and not significant to the SMBIOS specification, which is only concerned with the byte order. The following field

names, particularly for multiplexed fields, follow historical practice:

Offset	RFC 4122  Name	Length	Value	Description
00h	time_low	DWORD	Varies	The low field of the timestamp
04h	time_mid	WORD	Varies	The middle field of the timestamp
06h	time_hi_and_version	WORD	Varies	The high field of the timestamp multiplexed with the version number
08h	clock_seq_hi_and_reserved	BYTE	Varies	The high field of the clock sequence multiplexed with the variant
09h	clock_seq_low	BYTE	Varies	The low field of the clock sequence
0Ah	Node	6 BYTEs	Varies	The spatially unique node identifier

Although RFC 4122 recommends network byte order for all fields, the PC industry (including the ACPI, UEFI, and

Microsoft specifications) has consistently used little-endian byte encoding for the first three fields: time_low,

time_mid, time_hi_and_version. The same encoding, also known as wire format, should also be used for the

SMBIOS representation of the UUID.

The UUID {00112233-4455-6677-8899-AABBCCDDEEFF} would thus be represented as 33 22 11 00 55 44 77 66

88 99 AA BB CC DD EE FF.

If the value is all FFh, the ID is not currently present in the system, but can be set. If the value is all 00h, the ID is

not present in the system.