by Dinesh Thakur

A particular method of specifying the OPERAND for a MACHINE CODE instruction for some computer processors.

The simplest possible addressing modes are: REGISTER ADDRESSING, in which the operand is actually present in the specified register; IMMEDIATE ADDRESSING, where the operand value is supplied as part of the instruction, and ABSOLUTE ADDRESSING, also called direct addressing, where the memory address of the operand is given as part of the instruction.

Other commonly supported modes are: REGISTER INDIRECT, where the operand is to be found at the address contained in a specified register; and INDEXED ADDRESSING, where the operand address is calculated by adding an offset to a BASE ADDRESS contained in a register. There are dozens, if not hundreds, of possible addressing modes, and different processors vary widely in the number and kind that they support.