From Wikipedia- needs editing for AppleTV specific utilization"
A UUID is essentially a 16-byte (128-bit) number. In its canonical hexadecimal form a UUID may look like this:
The number of theoretically possible UUIDs is therefore 2128 = 25616 or about 3.4 × 1038. This means that 1 trillion UUIDs have to be created every nanosecond for 10 billion years to exhaust the number of UUIDs.
UUIDs are documented as part of ISO/IEC 11578:1996 "Information technology -- Open Systems Interconnection -- Remote Procedure Call (RPC)" and more recently in ITU-T Rec. X.667 | ISO/IEC 9834-8:2005 (freely available). The IETF has published Proposed Standard RFC 4122 that is technically equivalent with ITU-T Rec. X.667 | ISO/IEC 9834-8.