Q. Explain about Operand Address Calculation?

In actual machines effective address can be a register address, memory or I/O port address. Register reference instructions for example complement R1, clear R2 etc.usually don't need any memory reference (presuming register indirect addressing isnot being used) and can directly go to execute cycle. However memory reference instruction can use various addressing modes. Relying on type of addressing effective address (EA) of operands in memory is calculated. Calculation of effective address may require more memory fetches (for example in case of indirect addressing) so in this step we may calculate effective address as below: 

So the address part of IR now comprises the effective address which is direct address of operand.