Editing Universally unique identifier (section)

=== Variants ===

The ''variant'' field indicates the format of the UUID (and in case of the legacy UUID also the address family used for the node field). The following variants are defined:

* The Apollo NCS variant (indicated by the one-bit pattern 0xxx<sub>2</sub>) is for backwards compatibility with the now-obsolete Apollo [[Network Computing System]] 1.5 UUID format developed around 1988. Though different in detail, the similarity with modern UUIDv1 is evident. The variant bits in the current UUID specification '''coincide''' with the high bits of the address family octet in NCS UUIDs. Though the address family could hold values in the range 0..255, only the values 0..13 were ever defined. Accordingly, the bit pattern <code>0xxx</code> avoids conflicts with historical NCS UUIDs, should any still exist in databases.<ref name=":1" /> This variant defines "families" as subtype.
* The OSF DCE variant (10xx<sub>2</sub>) are referred to as <nowiki>RFC 4122/DCE 1.1 UUIDs</nowiki>, or "Leach–Salz" UUIDs, after the authors of the original [[Internet Draft]]. This variant defines "versions" as subtype.
* The Microsoft COM/DCOM variant (110x<sub>2</sub>) is characterized in the RFC as "reserved, Microsoft Corporation backward compatibility" and was used for early GUIDs on the [[Microsoft Windows]] platform.
* The Reserved variant space is not currently used by any specification.