Universally unique identifier
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A universally unique identifier UUID is a bit number used to identify information in computer systems. The term globally unique identifier GUID is globale binare used.
When generated according to the standard methods, UUIDs are for practical purposes unique, without depending for their uniqueness on a central registration authority or coordination between the parties generating them, unlike most other numbering schemes.
While the probability that a UUID will be duplicated is not zero, it is close enough to zero to be negligible. Thus, anyone can create a UUID and use it to identify something with near certainty that the identifier does not duplicate one that has already been, or will be, created to identify something else. Information labeled with UUIDs by independent parties can therefore be later combined into a single database, or transmitted on the same channel, without needing to resolve conflicts between identifiers.
Adoption of UUIDs and GUIDs globale binare widespread, with globale binare computing platforms globale binare support for generating them, and for parsing their textual representation. In its canonical textual representation, the sixteen octets of a UUID are represented as 32 hexadecimal base 16 digits, displayed in five groups separated by hyphens, in the form for a total of 36 characters 32 alphanumeric characters and four hyphens.
The canonical format string is based on the "record layout" for the 16 bytes of the UUID: This format should not be confused with " Windows Registry format", which refers to the format within the curly braces. The binary encoding of UUIDs varies between systems. Many systems encode the UUID entirely in a big-endian format. For example, aabbccddeeff is encoded as the bytes 00 11 22 33 44 55 66 77 88 99 globale binare bb cc dd ee ff.
For example, aabbccddeeff is encoded as the bytes 33 22 11 00 55 44 77 66 88 99 aa bb cc dd ee ff. In this format, the first 6 octets of the UUID are a bit timestamp the number of 4 microsecond units of time since 1 Jan UTC ; the next 1 trade binare optionen richtige octets are reserved; the next octet is the "address family"; and the final 7 octets are a bit host ID in the form globale binare by the address family.
Though different in detail, the similarity with modern version 1 UUIDs is globale binare. Though the address family could hold values in globale binare range The other two variants, variants 1 and 2, are used by the current UUID specifications. Variant bits aside, the two variants are the same except that when reduced to a binary form for storage or transmission, variant globale binare UUIDs use "network" big-endian byte order, while variant 2 GUIDs use "native" little-endian byte order.
In their textual representations, variants 1 and 2 are the same except for the variant bits. When byte swapping is required to globale binare between the big-endian byte order of variant 1 and the little-endian byte order of variant 2, the fields above define the swapping.
The first three fields are unsigned and bit integers and are subject to swapping, while the last two fields consist of uninterpreted globale binare, not subject to swapping. For both variants 1 and 2, five "versions" are defined in the standards, and each version may be globale binare appropriate than the others in specific use cases. Version is indicated by the M in the string representation. Version 1 UUIDs are generated from a time and a node id usually the MAC address ; version 2 UUIDs are generated from an identifier usually a group or user idtime, and a node id; versions 3 and 5 produce deterministic UUIDs generated by hashing a namespace identifier and name; and version 4 UUIDs are generated using a random or pseudo-random number.
Version 1 concatenates the bit MAC address of the "node" that is, the computer generating the UUIDwith a bit timestamp, being the globale binare of nanosecond intervals since midnight 15 October Coordinated Universal Time UTCthe globale binare on which the Gregorian calendar was first adopted.
RFC states globale binare the time value rolls over globale binare AD,  depending on the algorithm used, which implies that the bit timestamp is a signed quantity. However some software, such as the libuuid library, treats the timestamp as unsigned, putting the rollover time in AD.
A or bit "uniquifying" clock sequence extends the timestamp in order to handle cases where the processor clock does not advance fast enough, or where there are multiple processors and UUID generators per node. With each version 1 UUID corresponding to a single point in space the node and time intervals and clock sequencethe chance of two properly-generated version 1 UUID's being unintentionally the same is practically nil.
Since the time and clock sequence total 74 bits, 2 74 1. Usage of the node's network card MAC address for the node id means that a version 1 UUID globale binare be tracked back to the computer that created it.
Documents can sometimes be traced to the computers where they were created or edited through UUIDs embedded into them by word processing software. This privacy hole was used when locating the creator of the Melissa virus. Globale binare that case, the RFC requires that the least significant bit of the first octet of the node globale binare should be set to 1.
For this reason, many UUID implementations omit version 2. Version 2 UUIDs are similar to version 1, except that globale binare least significant 8 bits of the clock sequence are replaced by a "local domain" number, and the least significant 32 bits of the timestamp are replaced by an integer identifier meaningful within the specified local domain.
On the other hand, with the clock value truncated to the 28 most significant bits, compared to 60 bits in version 1, the clock in a version 2 UUID will "tick" only once every Version 3 and 5 UUIDs are generated by hashing a namespace identifier and name. The namespace identifier is itself a UUID. To determine the version 3 UUID corresponding to a given namespace and name, the UUID of the namespace globale binare transformed to a string of bytes, concatenated with the input name, then hashed with MD5, yielding bits.
Six or seven bits are then replaced by fixed values, the 4-bit version e. Since 6 or 7 bits are thus predetermined, only globale binare bits contribute to the uniqueness of the UUID. Globale binare SHA1 generates bit digests, the digest is truncated to bits before the version and variant bits are inserted. However, neither the namespace nor name can be determined from the UUID, given the other, except by brute-force search. A version 4 UUID is randomly generated. As in other UUIDs, four bits are used to indicate version 4, and 2 or 3 bits to indicate the variant 10 or for variants 1 and 2, respectively.
Globale binare, for variant 1 that globale binare, most UUIDs a random version 4 UUID will have 6 predetermined variant and version bits, leaving bits for the randomly-generated part, for a total of 2or 5. There are half as many possible version 4 variant 2 UUIDs legacy GUIDs because there is one less random bit available, 3 bits being consumed for the variant.
Some pseudorandom number generators lack necessary entropy to produce sufficiently pseudorandom numbers. If this is not feasible, the namespace variant should be used. Collision occurs when globale binare same UUID is generated more than once and assigned to different globale binare. In the case of standard version 1 and 2 UUIDs using unique MAC addresses from network cards, collisions can occur only when an implementation varies from the standards, either inadvertently or intentionally.
In contrast globale binare version 1 and 2 UUIDs using randomly-generated node ids, hash-based version 3 and 5 UUIDs, and random version 4 UUIDs, globale binare can occur even without implementation problems, albeit with a probability so small that it can normally be ignored. This probability can be computed precisely based on analysis of the birthday problem. This number is equivalent to generating 1 billion UUIDs per second for about 85 years, and a file containing this many UUIDs, at 16 bytes per UUID, would be about 45 exabytes, many times larger than the largest databases currently in existence, which are on the order of hundreds of petabytes.
The smallest number of version 4 UUIDs which must be generated for the probability of finding a collision to be p is approximated by the formula:. Thus, for there to be a one in a billion chance of duplication, trillion version 4 UUIDs globale binare be generated. One of the uses of UUIDs in Solaris using Globale binare Software Foundation implementation is identification of a running operating system instance for the purpose of pairing crash globale binare data with Fault Management Event in the case of kernel panic.
UUIDs are commonly used as a unique key in database tables. Instead, it returns a byte bit RAW value based on a host identifier and a process or thread identifier, somewhat similar to a GUID.
The random nature of standard version 3, 4, and 5 UUIDs and the ordering of the fields within standard version 1 and 2 UUIDs may create problems with database locality or performance when UUIDs are used as primary keys. For example, in Jimmy Nilsson reported a significant improvement in performance with Microsoft SQL Server when the version 4 UUIDs being used as keys were modified to include a non-random globale binare based on system time.
Globale binare Wikipedia, the free encyclopedia. Internet Engineering Task Force. Authentication and Security Services". Retrieved 9 January Retrieved 23 January Society for Globale binare and Applied Mathematics. Windows Dev Center globale binare Desktop app technologies.
Retrieved 15 December globale binare You reference an interface at run time with a globally unique globale binare identifier IID. This IID, globale binare is a specific instance of a globally unique identifier GUID supported by COM, allows a client to ask an object precisely whether it supports the semantics of the interface, without unnecessary overhead and without the confusion that could arise in a system from having multiple versions of the same interface with the same name.
A listing of the CATIDs and the human-readable names globale binare stored in a well-known location in the registry. Retrieved from " https: Unique identifiers Windows administration.