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ASCII was developed from telegraph code. Its first commercial use was as a seven-bit teleprinter code promoted by Bell data services.


Work on the ASCII standard began on October 6, 1960, with the first meeting of the American Standards Association's (ASA).ASCII stands for American Standard Code for Information Interchange)  and uses 7 bits to represent each character. This allows for 27 = 128 codes to be used for letters, symbols, numbers, etc. that appear in the English language.


Unicode is an information technology (IT) standard for the consistent encoding, representation, and handling of text expressed in most of the world's writing systems. The standard is maintained by the Unicode Consortium, and as of March 2020, there is a repertoire of 143,859 characters, with Unicode 13.0 (these characters consist of 143,696 graphic characters and 163 format characters) covering 154 modern and historic scripts, as well as multiple symbol sets and emoji.


EBCDIC was devised in 1963 and 1964 by IBM and was announced with the release of the IBM System/360 line of mainframe computers. It is an eight-bit character encoding, developed separately from the seven-bit ASCII encoding scheme. It was created to extend the existing Binary-Coded Decimal (BCD) Interchange Code, or BCDIC, which itself was devised as an efficient means of encoding the two zone and number punches on punched cards into six bits.


You may find the following resource for ACSII, Unicode and other character encoding useful:

ASCII to CHAR (Code it)