Alphanumeric Codes | ASCII code | EBCDIC Code | UNICODE

What is Alphanumeric Code?

Alphanumeric codes are character-encoding conventions that represent letters, numbers and other text elements as numeric values. Computers store and transmit those values as binary data. The term character code is broader because it also covers punctuation, control functions and symbols.

A keyboard sends key events or scan codes, and software interprets them as text according to the active layout and character encoding. A display then renders glyphs for the decoded characters. Mouse input describes actions and positions rather than encoded text.

Hollerith-derived punched-card systems were an early form of machine-readable data. A later IBM card had 80 columns and 12 row positions, with a pattern of holes in a column representing a character. Calling this simply a 12-bit code hides the physical card format and the different coding conventions used over time.

Punched cards once carried data and program instructions into tabulating machines and computers. They are now a legacy storage medium, while software systems use electronic character encodings for text interchange.

The sections below compare ASCII, the EBCDIC code-page family and Unicode. ASCII remains an important 7-bit foundation, EBCDIC remains in use on some IBM systems, and Unicode supplies the common character repertoire used by modern encoding forms such as UTF-8.

ASCII Code

ASCII code stands for American Standard Code for Information Interchange. It is a 7-bit coded character set for English letters, decimal digits, punctuation and control functions.

Seven bits provide 128 values, numbered 0 to 127. The excerpt below lists values 0 to 15. Its BIN column pads each 7-bit ASCII value with a leading zero so that the entries appear as full 8-bit bytes.

This excerpt contains only the first 16 ASCII control values. In its final two rows, SO means Shift Out and SI means Shift In; XON is the separate DC1 control at decimal 17. The full set also includes the remaining control values, space, punctuation, digits, uppercase and lowercase English letters plus DEL.

EBCDIC Code

EBCDIC stands for Extended Binary Coded Decimal Interchange Code. IBM developed it in 1963, and EBCDIC code pages remain in use on systems including IBM zSystems and iSeries. A single-byte EBCDIC code page has 256 possible byte values, but EBCDIC is a family of code pages rather than one universal character map. Letters and digits are invariant across common pages, while some punctuation and national characters vary. The table below shows selected invariant values from EBCDIC code.

Unicode

Unicode assigns each encoded character a code point in a shared code space from U+0000 to U+10FFFF. The code space contains 1,114,112 code points, although not every point is assigned to a character. In Unicode 17.0, 159,801 characters are assigned. UTF-8, UTF-16 and UTF-32 encode the same code points with different code-unit sequences, so a code point is not the same as a stored byte or a displayed glyph. The table below is a legacy illustration, not an authoritative chart. In particular, its 0080 row shows Windows-1252-style printable mappings, but Unicode assigns U+0080 to U+009F as C1 control code points. Use the Unicode Consortium’s current code charts for exact assignments.