This document discusses various data representation techniques including excess-3 code, Gray code, binary coded decimal, ASCII, EBCDIC, Unicode, and logic gates. Excess-3 code represents each decimal number as a binary number in excess of three. Gray code ensures each code differs from its neighbor by one bit. ASCII and EBCDIC are character encoding standards that allow representation of text. Unicode supports encoding for many languages. The document also describes logic gates like AND, OR, NOT, XOR, and how logic expressions can be represented using gates.