UUIDs (as GUIDs) in Windows predate RFC 4122, so I don't think it's that unreasonable that they're not compliant with the spec (since the exact contents of a UU

UUIDs (as GUIDs) in Windows predate RFC 4122, so I don't think it's that unreasonable that they're not compliant with the spec (since the exact contents of a UUID aren't typically that important, but consistency in how you produce them is). The GUID implementation in Windows derives from the DCE RPC specification [1]. That's where the multibyte integers in the RFC 4122 specification come from (they're stated the same way in the DCE RPC spec), and it doesn't explicitly specify their endianness. It does call them "NDR integers", but NDR integers can be little endian or big endian depending on implementation. DCE specifies a mechanism by which you'd indicate which you're using in an RPC call, but that data's not included in the UUID format-- you get whatever byte order the system's decided to use, which, for Windows, is little-endian. [1] https://pubs.opengroup.org/onlinepubs/9629399/apdxa.htm#tagcjh_20 https://pubs.opengroup.org/onlinepubs/9629399/apdxa.htm#tagc...