Basic of Addresing modes

Before going into details, let's talk informally. Cool?

Assume that your girlfriend told you to meet at A. and you don't know what A is?

So there are few possibilities what A may be:

  • It might be the address of some restaurants.
  • It may be the address of some Hotel or maybe some Hill station name.

So before going to meet your girlfriend, you must know what A is?

The same case happens here.

I say  "Add 8" 

here we don't know what 8 represent.

  • It may be the id_number of some particular register where our operand is present.
  • It may be the operand itself.
  • It may be the address of our operand directly.

So the Entire purpose of reading Addressing mode is to calculate Effective address.

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.

Effective Address:  The actual address of our operand.