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A serial number is a unique number that is one of a series assigned for identification which varies from its successor or predecessor by a fixed discrete integer value. Common usage has expanded the term to refer to any unique alphanumeric identifier for one of a large set of objects, however in data processing and allied fields in computer science. Not every numerical identifier is a serial number; identifying numbers which are not serial numbers are sometimes called nominal numbers. Sequence numbers are almost always non-negative, and typically start at zero or one.
Applications of serial numbering Serial numbers are valuable in quality control, as once a defect is found in the production of a particular batch of product, the serial number will quickly identify which units are affected. Serial numbers are also used as a deterrent against theft and counterfeit products in that serial numbers can be recorded, and stolen or otherwise irregular goods can be identified. Many computer programs come with serial numbers, often called "CD keys," and the installers often require the user to enter a valid serial number to continue. These numbers are verified using a certain algorithm to avoid usage of counterfeit keys. Serial numbers also help track down counterfeit currency, because in some countries each banknote has a unique serial number. The ISSN or International Standard Serial Number seen on magazines and other periodicals, an equivalent to the ISBN applied to books, is serially assigned but takes its name from the library science use of serial to mean a periodical. Certificates and Certificate Authorities (CA) are necessary for widespread use of cryptography. These depend on applying mathematically rigorous serial numbers and serial number arithmetic The term "serial number" is also used in military formations as an alternative to the expression "service number". Estimating population size from serial numbers If there are items whose serial numbers is part of a sequence of consecutive numbers and you take n number of random samples of items' serial numbers, you can then estimate the population of items "in the wild" using a maximum likelihood method derived using Bayesian reasoning. Serial number arithmetic Serial numbers are often used in network protocols. However, most sequence numbers in computer protocols are limited to a fixed number of bits, and will wrap around after a sufficiently many numbers have been allocated. Thus, recently-allocated serial numbers may duplicate very old serial numbers, but not other recently-allocated serial numbers. To avoid ambiguity with these non-unique numbers, RFC 1982, " Serial Number Arithmetic" defines special rules for calculations involving these kinds of serial numbers. Lollipop sequence number spaces are a more recent and sophisticated scheme for dealing with finite-sized sequence numbers in protocols. See also | ||||||||
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