what is addressing mode

Addressing mode is an aspect of the instruction set architecture in most central processing unit (CPU) designs. It defines how the machine language instructions in that architecture identify the operand(s) of each instruction. An addressing mode specifies how to calculate the effective memory address of an operand by using information held in registers and/or constants contained within a machine instruction or elsewhere. In computer programming, addressing modes are primarily of interest to those who write in assembly languages and to compiler writers. There are different types of addressing modes, such as immediate mode, register mode, register indirect mode, autoincrement mode, and indexed addressing mode. The effective address refers to the address of an exact memory location in which an operand’s value is actually present. The addressing modes help us specify the way in which an operand’s effective address is represented in any given instruction.