Difference between Direct and Immediate Addressing Modes

Prerequisite – Addressing Modes

1. Direct Addressing Mode: In direct addressing mode, the address field contains the address of the operand.

Effective Address (EA) = address field of operand 

Example: Add the contents of register 1303 to the accumulator.

Add (1303) 

Only a single memory reference is required to access data. So no additional calculations are required to work out the effective address. 

2. Immediate Addressing Mode: In immediate addressing mode, the operand is a part of the instruction.

Here the Operand = Address Field 

Example: Add 3 to the accumulator.

ADD 3

No memory reference is required to fetch data. So no additional calculations are required to work out the effective address. It is a fast method. But the downside is that it has a limited range. Now let’s compare Direct and Immediate addressing modes.

S. No.	Parameters	Direct Addressing Mode	Immediate Addressing Mode
1.	Address Field	Address fields contain the effective address of the operand.	There is no address field as an operand is a part of the instruction. In place of address field, immediate addressing mode has operand field.
2.	Memory Referencing	It requires one reference to memory.	It does not require any reference to memory.
3.	Process Speed	It is slower compared to the immediate mode.	It is faster compared to the direct addressing mode.
4.	Range	It has more range than in immediate mode.	It has a limited range.
5.	Example	Add (1303)	ADD 3
6.	Advantage	Easy as direct reference to memory	There is no memory reference for fetching data.
7.	Disadvantage	Restricted address space	Constrained operand magnitude
8.	Application	It assists in accessing static data and implementing variables.	Set the register to a constant value.

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