Is there any difference between a GUID and a UUID

Question

I see these 2 acronyms thrown around  and I was wondering if there are any differences between a GUID and a UUID

User · Answer

GUID is Microsoft s implementation of the UUID standard   Per Wikipedia      The term GUID usually refers to Microsoft s implementation of the Universally Unique Identifier  UUID  standard    An updated quote from that same Wikipedia article      RFC 4122 itself states that UUIDs  are also known as GUIDs   All this suggests that  GUID   while originally referring to a variant of UUID used by Microsoft  has become simply an alternative name for UUID

User · Answer

Not really  GUID is more Microsoft-centric whereas UUID is used more widely  e g   as in the urn uuid  URN scheme  and in CORBA

User · Answer

GUID has longstanding usage in areas where it isn t necessarily a 128-bit value in the same way as a UUID  For example  the RSS specification defines GUIDs to be any string of your choosing  as long as it s unique  with an  isPermalink  attribute to specify that the value you re using is just a permalink back to the item being syndicated

User · Answer

The simple answer is    no difference  they are the same thing  2020-08-20 Update  While GUIDs  as used by Microsoft  and UUIDs  as defined by RFC4122  look similar and serve similar purposes  there are subtle-but-occasionally-important differences   Specifically  some Microsoft GUID docs allow GUIDs to contain any hex digit in any position  while RFC4122 requires certain values for the version and variant fields   Also   per that same link   GUIDs should be all-upper case  whereas UUIDs should be  quot output as lower case characters and are case insensitive on input quot    This can lead to incompatibilities between code libraries  such as this    Original answer follows   Treat them as a 16 byte  128 bits  value that is used as a unique value   In Microsoft-speak they are called GUIDs  but call them UUIDs when not using Microsoft-speak  Even the authors of the UUID specification and Microsoft claim they are synonyms   From the introduction to IETF RFC 4122  quot A Universally Unique IDentifier  UUID  URN Namespace quot    quot a Uniform Resource Name namespace for UUIDs  Universally Unique IDentifier   also known as GUIDs  Globally Unique IDentifier   quot   From the ITU-T Recommendation X 667  ISO IEC 9834-8 2004 International Standard   quot UUIDs are also known as Globally Unique Identifiers  GUIDs   but this term is not used in this Recommendation  quot   And Microsoft even claims a GUID is specified by the UUID RFC   quot In Microsoft Windows programming and in Windows operating systems  a globally unique identifier  GUID   as specified in  RFC4122   is     The term universally unique identifier  UUID  is sometimes used in Windows protocol specifications as a synonym for GUID  quot    But the correct answer depends on what the question means when it says  quot UUID quot     The first part depends on what the asker is thinking when they are saying  quot UUID quot   Microsoft s claim implies that all UUIDs are GUIDs  But are all GUIDs real UUIDs  That is  is the set of all UUIDs just a proper subset of the set of all GUIDs  or is it the exact same set  Looking at the details of the RFC 4122  there are four different  quot variants quot  of UUIDs   This is mostly because such 16 byte identifiers were in use before those specifications were brought together in the creation of a UUID specification  From section 4 1 1 of RFC 4122  the four variants of UUID are   Reserved  Network Computing System backward compatibility The variant specified in RFC 4122  of which there are five sub-variants  which are called  quot versions quot   Reserved  Microsoft Corporation backward compatibility Reserved for future definition   According to RFC 4122  all UUID variants are  quot real UUIDs quot   then all GUIDs are real UUIDs  To the literal question  quot is there any difference between GUID and UUID quot  the answer is definitely no for RFC 4122 UUIDs  no difference  but subject to the second part below   But not all GUIDs are variant 2 UUIDs  e g  Microsoft COM has GUIDs which are variant 3 UUIDs   If the question was  quot is there any difference between GUID and variant 2 UUIDs quot   then the answer would be yes -- they can be different  Someone asking the question probably doesn t know about variants and they might be only thinking of variant 2 UUIDs when they say the word  quot UUID quot   e g  they vaguely know of the MAC address time and the random number algorithms forms of UUID  which are both versions of variant 2   In which case  the answer is yes different  So the answer  in part  depends on what the person asking is thinking when they say the word  quot UUID quot   Do they mean variant 2 UUID  because that is the only variant they are aware of  or all UUIDs  The second part depends on which specification being used as the definition of UUID  If you think that was confusing  read the ITU-T X 667 ISO IEC 9834-8 2004 which is supposed to be aligned and fully technically compatible with RFC 4122   It has an extra sentence in Clause 11 2 that says   quot All UUIDs conforming to this Recommendation   International Standard shall have variant bits with bit 7 of octet 7 set to 1 and bit 6 of octet 7 set to 0 quot   Which means that only variant 2 UUID conform to that Standard  those two bit values mean variant 2   If that is true  then not all GUIDs are conforming ITU-T ISO IEC UUIDs  because conformant ITU-T ISO IEC UUIDs can only be variant 2 values  Therefore  the real answer also depends on which specification of UUID the question is asking about  Assuming we are clearly talking about all UUIDs and not just variant 2 UUIDs  there is no difference between GUID and IETF s UUIDs  but yes difference between GUID and conforming ITU-T ISO IEC s UUIDs  Binary encodings could differ When encoded in binary  as opposed to the human-readable text format   the GUID may be stored in a structure with four different fields as follows  This format differs from the  UUID standard  8 only in the byte order of the first 3 fields  Bits  Bytes Name   Endianness  Endianness                     GUID       RFC 4122  32    4     Data1  Native      Big 16    2     Data2  Native      Big 16    2     Data3  Native      Big 64    8     Data4  Big         Big

User · Answer

Microsoft s GUID s textual representation can be in the form of a UUID being surrounded by two curly braces

User · Answer

GUID is Microsoft s implementation of the UUID standard   Per Wikipedia      The term GUID usually refers to Microsoft s implementation of the Universally Unique Identifier  UUID  standard    An updated quote from that same Wikipedia article      RFC 4122 itself states that UUIDs  are also known as GUIDs   All this suggests that  GUID   while originally referring to a variant of UUID used by Microsoft  has become simply an alternative name for UUID

User · Answer

Not really  GUID is more Microsoft-centric whereas UUID is used more widely  e g   as in the urn uuid  URN scheme  and in CORBA

User · Answer

One difference between GUID in SQL Server and UUID in PostgreSQL is letter case  SQL Server outputs upper while PostgreSQL outputs lower   The hexadecimal values  a  through  f  are output as lower case characters and are case insensitive on input  - rfc4122 section-3

User · Answer

The simple answer is    no difference  they are the same thing  2020-08-20 Update  While GUIDs  as used by Microsoft  and UUIDs  as defined by RFC4122  look similar and serve similar purposes  there are subtle-but-occasionally-important differences   Specifically  some Microsoft GUID docs allow GUIDs to contain any hex digit in any position  while RFC4122 requires certain values for the version and variant fields   Also   per that same link   GUIDs should be all-upper case  whereas UUIDs should be  quot output as lower case characters and are case insensitive on input quot    This can lead to incompatibilities between code libraries  such as this    Original answer follows   Treat them as a 16 byte  128 bits  value that is used as a unique value   In Microsoft-speak they are called GUIDs  but call them UUIDs when not using Microsoft-speak  Even the authors of the UUID specification and Microsoft claim they are synonyms   From the introduction to IETF RFC 4122  quot A Universally Unique IDentifier  UUID  URN Namespace quot    quot a Uniform Resource Name namespace for UUIDs  Universally Unique IDentifier   also known as GUIDs  Globally Unique IDentifier   quot   From the ITU-T Recommendation X 667  ISO IEC 9834-8 2004 International Standard   quot UUIDs are also known as Globally Unique Identifiers  GUIDs   but this term is not used in this Recommendation  quot   And Microsoft even claims a GUID is specified by the UUID RFC   quot In Microsoft Windows programming and in Windows operating systems  a globally unique identifier  GUID   as specified in  RFC4122   is     The term universally unique identifier  UUID  is sometimes used in Windows protocol specifications as a synonym for GUID  quot    But the correct answer depends on what the question means when it says  quot UUID quot     The first part depends on what the asker is thinking when they are saying  quot UUID quot   Microsoft s claim implies that all UUIDs are GUIDs  But are all GUIDs real UUIDs  That is  is the set of all UUIDs just a proper subset of the set of all GUIDs  or is it the exact same set  Looking at the details of the RFC 4122  there are four different  quot variants quot  of UUIDs   This is mostly because such 16 byte identifiers were in use before those specifications were brought together in the creation of a UUID specification  From section 4 1 1 of RFC 4122  the four variants of UUID are   Reserved  Network Computing System backward compatibility The variant specified in RFC 4122  of which there are five sub-variants  which are called  quot versions quot   Reserved  Microsoft Corporation backward compatibility Reserved for future definition   According to RFC 4122  all UUID variants are  quot real UUIDs quot   then all GUIDs are real UUIDs  To the literal question  quot is there any difference between GUID and UUID quot  the answer is definitely no for RFC 4122 UUIDs  no difference  but subject to the second part below   But not all GUIDs are variant 2 UUIDs  e g  Microsoft COM has GUIDs which are variant 3 UUIDs   If the question was  quot is there any difference between GUID and variant 2 UUIDs quot   then the answer would be yes -- they can be different  Someone asking the question probably doesn t know about variants and they might be only thinking of variant 2 UUIDs when they say the word  quot UUID quot   e g  they vaguely know of the MAC address time and the random number algorithms forms of UUID  which are both versions of variant 2   In which case  the answer is yes different  So the answer  in part  depends on what the person asking is thinking when they say the word  quot UUID quot   Do they mean variant 2 UUID  because that is the only variant they are aware of  or all UUIDs  The second part depends on which specification being used as the definition of UUID  If you think that was confusing  read the ITU-T X 667 ISO IEC 9834-8 2004 which is supposed to be aligned and fully technically compatible with RFC 4122   It has an extra sentence in Clause 11 2 that says   quot All UUIDs conforming to this Recommendation   International Standard shall have variant bits with bit 7 of octet 7 set to 1 and bit 6 of octet 7 set to 0 quot   Which means that only variant 2 UUID conform to that Standard  those two bit values mean variant 2   If that is true  then not all GUIDs are conforming ITU-T ISO IEC UUIDs  because conformant ITU-T ISO IEC UUIDs can only be variant 2 values  Therefore  the real answer also depends on which specification of UUID the question is asking about  Assuming we are clearly talking about all UUIDs and not just variant 2 UUIDs  there is no difference between GUID and IETF s UUIDs  but yes difference between GUID and conforming ITU-T ISO IEC s UUIDs  Binary encodings could differ When encoded in binary  as opposed to the human-readable text format   the GUID may be stored in a structure with four different fields as follows  This format differs from the  UUID standard  8 only in the byte order of the first 3 fields  Bits  Bytes Name   Endianness  Endianness                     GUID       RFC 4122  32    4     Data1  Native      Big 16    2     Data2  Native      Big 16    2     Data3  Native      Big 64    8     Data4  Big         Big

User · Answer

One difference between GUID in SQL Server and UUID in PostgreSQL is letter case  SQL Server outputs upper while PostgreSQL outputs lower   The hexadecimal values  a  through  f  are output as lower case characters and are case insensitive on input  - rfc4122 section-3

User · Answer

Not really  GUID is more Microsoft-centric whereas UUID is used more widely  e g   as in the urn uuid  URN scheme  and in CORBA

User · Answer

GUID has longstanding usage in areas where it isn t necessarily a 128-bit value in the same way as a UUID  For example  the RSS specification defines GUIDs to be any string of your choosing  as long as it s unique  with an  isPermalink  attribute to specify that the value you re using is just a permalink back to the item being syndicated

User · Answer

Microsoft s GUID s textual representation can be in the form of a UUID being surrounded by two curly braces

User · Answer

GUID is Microsoft s implementation of the UUID standard   Per Wikipedia      The term GUID usually refers to Microsoft s implementation of the Universally Unique Identifier  UUID  standard    An updated quote from that same Wikipedia article      RFC 4122 itself states that UUIDs  are also known as GUIDs   All this suggests that  GUID   while originally referring to a variant of UUID used by Microsoft  has become simply an alternative name for UUID

User · Answer

GUID is Microsoft s implementation of the UUID standard   Per Wikipedia      The term GUID usually refers to Microsoft s implementation of the Universally Unique Identifier  UUID  standard    An updated quote from that same Wikipedia article      RFC 4122 itself states that UUIDs  are also known as GUIDs   All this suggests that  GUID   while originally referring to a variant of UUID used by Microsoft  has become simply an alternative name for UUID

User · Answer

Not really  GUID is more Microsoft-centric whereas UUID is used more widely  e g   as in the urn uuid  URN scheme  and in CORBA

[guid] Is there any difference between a GUID and a UUID?

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