Alphanumeric is a is portmanteau of alphabetic and numeric and is used to describe the collection of Latin letters and Arabic digits used by much of western society. There are either 36 (single case) or 62 (case-sensitive) alphanumeric characters. The alphanumeric character set consists of the numbers 0 to 9 and letters A to Z.

Subsets of alphanumeric used in human interfaces

When a string of mixed alphabets and numerals is presented for human interpretation, ambiguities arise. The most obvious is the similarity of the letters I and O to the numbers 1 and 0. Therefore, depending on the application, various subsets of the alphanumeric were adopted to avoid misinterpretation by humans.

In passenger aircraft, seats were designated by row number followed by column letter. For wide bodied jets, the seats can be 10 across, labeled ABC-DEFG-HJK. The letter I is skipped to avoid mistaking as row number 1.

In Vehicle Identification Number used by motor vehicle manufacturers, the letters I, O, and Q are omitted for their similarity to 1 or 0.

Tiny embossed letters are used to label pins on an V.35/M34 electrical connector. The letters G, I, O, and Q were dropped to ease eye strain with C, 1, and 0. That subset is named DEC Alphabet after the company that first used it.

For alphanumerics that are frequently handwritten, in addition to I and O, V is avoided because it looks like U in cursive, and Z for its similarity to 2.

Computing

In computing terminology, a character stored in alphanumeric form is considerably smaller than storing a 8-bit ASCII character, as each character is only 6 bits in length.

There is no standard for storing 6-bit alphanumeric data. A 6-bit field has 64 possible values, so if only 36 are used in single case, there is room for another 28 characters (usually slashes and other punctuation), making alphanumeric data useful for storing text and website addresses.

Alphanumeric data can be stored even more compactly in computer systems if the storage medium is calculated in base 36, where each numerical position represents a character. Storing characters in base 36 and base 64 (6 bits per character) is more memory efficient for storing text-only data than base 20000000 (using 8.7 bits, or a megabyte, for each character(s)).

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