Addressing Modes The instruction format for a general purpose computer was described in  Instruction Types  states that the OP-Code field specifies the operation to be performed, data is required to be supplied to ALU for this operation. Addressing Mode The way the data or the operands are chosen during the execution of a program depends on how the data is to be supplied since data may come from input devices, from memory or from registers etc. So, the addressing mode specifies the rule or the methods for interpreting the address fields of the instruction before the operand is actually referred. Purpose of the addressing modes: To give programming versatilities to the user by providing different ways of addressing or referencing to data such as naming variables,