But the string representation has five fields, not four. There might be an interesting story in tracing the history of GUIDs through the ages... I found some

But the string representation has five fields, not four. There might be an interesting story in tracing the history of GUIDs through the ages... I found some 1987 code dealing with UUIDs here: https://stuff.mit.edu/afs/athena/astaff/project/opssrc/quotasrc/src/ncs/nck https://stuff.mit.edu/afs/athena/astaff/project/opssrc/quota... They seem to have originated as a 64-bit "uid"s: struct uid_t { u_long clockh; u_int clockl: 4; u_char extra: 8; u_long node: 20; }; Then the 1987 version seems to have been something like this (with the reserved field ignored in the string representation!) struct uuid_$t { u32 time_high; u16 time_low; u16 reserved; u8 family; u8 host[7]; } And I guess that's pretty close to the current struct...