A defined list of characters recognized by the computer hardware and software. Each character is represented by a number. The ASCII character set, for example, uses the numbers 0 through 127 to represent all English characters as well as special control characters. European ISO character sets are similar to ASCII, but they contain additional characters for European languages.
Data Representation This is Chapter 1 of Randall Hyde's book, "Art of Assembly Language." It describes the binary and hexadecimal numbering systems, binary data organization (bits, nibbles, bytes, words, and double words), signed and unsigned numbering systems, arithmetic, logical, shift, and rotate operations on binary values, bit fields and packed data, and the ASCII character set.