Convert between common UUID formats, generate new values and analyze their byte components. What is UUID?
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A UUID or ‘Universally Unique Identifier’ (also known as a GUID) is a 128-bit label used to identify resources. The UUID specification has 5 versions, each one has its own generation strategy with v4 being random or pseudo-random numbers.
The term GUID or ‘Globally Unique Identifier’ is generally used when working with Microsoft technologies.
Read the UUID specification for more info.
In the case of v1 and v2 UUIDs using unique MAC addresses as their node, generating duplicates is virtually imposible. In contrast, all other standard versions can have collisions. However the probability of generating a duplicate UUID is extremely low.
For example, the number of random v4 UUIDs which need to be generated in order to have a chance of one collision is 2.71 quintillion. This number is equivalent to generating 1 billion UUIDs per second for about 86 years.
A UUID is defined in fields that are integral numbers of octets. The fields are encoded as 16 octets with each field encoded with the Most Significant Byte first (known as network byte order).
| Field | Data Type | Octets | Description |
|---|---|---|---|
| time_low | uint32 | 0-3 | The low field of the timestamp |
| time_mid | uint16 | 4-5 | The middle field of the timestamp |
| time_hi_and_version | uint16 | 6-7 | The high field of the timestamp multiplexed with the version number |
| clock_seq_hi_and_reserved | uint8 | 8 | The high field of the clock sequence multiplexed with the variant |
| clock_seq_low | uint8 | 9 | The low field of the clock sequence |
| node | uint48 | 10-15 | The spatially unique node identifier |