This is a list of some binary codes that are (or have been) used to represent
text as a sequence of
binary digits "0" and "1". Fixed-width binary codes use a set number of bits to represent each character in the text, while in
variable-width binary codes, the number of bits may vary from character to character.
Five-bit binary codes
Several different five-bit codes were used for early
punched tape systems.
Five bits per character only allows for 32 different characters, so many of the five-bit codes used two sets of characters per value referred to as FIGS (figures) and LTRS (letters), and reserved two characters to switch between these sets. This effectively allowed the use of 60 characters.
Braille – Braille characters are represented using six dot positions, arranged in a rectangle. Each position may contain a raised dot or not, so Braille can be considered to be a six-bit binary code.
ASCII – The ubiquitous ASCII code was originally defined as a seven-bit character set. The ASCII article provides a detailed set of equivalent standards and variants. In addition, there are various extensions of ASCII to eight bits (see
Eight-bit binary codes)
CCIR 476 – Extends ITA2 from 5 to 7 bits, using the extra 2 bits as
check digits[4]
AUTOSPEC – Also known as Bauer code. AUTOSPEC repeats a five-bit character twice, but if the character has odd parity, the repetition is inverted.[4]
Decabit – A datagram of electronic pulses which are transmitted commonly through power lines. Decabit is mainly used in Germany and other European countries.
UTF-8 – Encodes characters in a way that is mostly compatible with
ASCII but can also encode the full repertoire of Unicode characters with sequences of up to four 8-bit bytes.
UTF-16 – Extends UCS-2 to cover the whole of Unicode with sequences of one or two 16-bit elements
GB 18030 – A full-Unicode variable-length code designed for compatibility with older Chinese multibyte encodings
Huffman coding – A technique for expressing more common characters using shorter bit strings than are used for less common characters
Data compression systems such as
Lempel–Ziv–Welch can compress arbitrary binary data. They are therefore not binary codes themselves but may be applied to binary codes to reduce storage needs.
Other
Morse code is a variable-length telegraphy code, which traditionally uses a series of long and short pulses to encode characters. It relies on gaps between the pulses to provide separation between letters and words, as the letter codes do not have the
"prefix property". This means that Morse code is not necessarily a binary system, but in a sense may be a ternary system, with a 10 for a "dit" or a "dot", a 1110 for a dash, and a 00 for a single unit of separation. Morse code can be represented as a binary stream by allowing each bit to represent one unit of time. Thus a "dit" or "dot" is represented as a 1 bit, while a "dah" or "dash" is represented as three consecutive 1 bits. Spaces between symbols, letters, and words are represented as one, three, or seven consecutive 0 bits. For example, "NO U" in Morse code is "— .— — —. . —", which could be represented in binary as "1110100011101110111000000010101110". If, however, Morse code is represented as a ternary system, "NO U" would be represented as "1110|10|00|1110|1110|1110|00|00|00|10|10|1110".