In Computer Organization & Architecture (COA), Addressing Modes are one of the most repeated topics in ECET exams. Understanding these modes is crucial because they decide how the processor identifies the location of operands during instruction execution.
📘 Concept Notes – Addressing Modes
⚙️ What is Addressing Mode?
Addressing mode specifies how an operand (data) is chosen during instruction execution. Operand can be in CPU register, memory, or part of the instruction itself.
👉 Simply: Addressing mode tells “where to find the operand.”
Types of Addressing Modes
1️⃣ Immediate Addressing
- Operand is directly given in the instruction.
- Example:
MOV R1, #25→ Value25is directly in the instruction.
2️⃣ Register Addressing
- Operand is stored in a register.
- Example:
MOV R1, R2→ Contents of R2 moved to R1.
3️⃣ Direct Addressing
- Instruction contains memory address of operand.
- Example:
MOV R1, 5000→ Operand taken from memory location 5000.
4️⃣ Indirect Addressing
- Instruction contains address of a register/memory, which further holds the effective address of operand.
- Example:
MOV R1, (R2)→ R2 has the address, operand fetched from there.
5️⃣ Register Indirect Addressing
- Register contains the memory address of operand.
- Example:
MOV R1, (R3)→ Operand is in memory whose address is in R3.
6️⃣ Indexed Addressing
- Effective Address = Base Address + Index Value.
- Mostly used in arrays.
- Example:
MOV R1, A[5].
7️⃣ Relative Addressing
- Effective Address = Program Counter (PC) + displacement.
- Mostly used for branch instructions.
⚙️ Formula (General Effective Address Expression)
Where:
= Effective Address
= Address part of instruction
= Contents of register
🔟 10 Most Expected MCQs – ECET 2026 (COA – Addressing Modes)
Q1. In which addressing mode is the operand given inside the instruction itself?
A) Direct
B) Register
C) Immediate
D) Indirect
Q2. If the instruction is MOV R1, 5000, which addressing mode is used?
A) Direct
B) Immediate
C) Indirect
D) Indexed
Q3. Register Indirect Addressing mode means:
A) Operand is in register directly
B) Register contains address of operand
C) Operand is inside instruction
D) None
Q4. Which addressing mode is best suited for array implementation?
A) Immediate
B) Indexed
C) Register
D) Direct
Q5. Relative Addressing uses which register?
A) Accumulator
B) Program Counter
C) Instruction Register
D) Base Register
Q6. Convoy effect is related to which concept?
A) Addressing
B) Scheduling
C) Pipelining
D) Cache
Q7. Effective Address formula is:
A) EA = PC + Displacement
B) EA = A + (R)
C) Both A & B
D) None
Q8. Which addressing mode may cause two memory references?
A) Immediate
B) Direct
C) Indirect
D) Register
Q9. Which addressing mode is fastest?
A) Register
B) Indirect
C) Indexed
D) Relative
Q10. In assembly, MOV R1, (R2) represents:
A) Register
B) Direct
C) Register Indirect
D) Indexed
✅ Answer Key
| Q.No | Answer |
|---|---|
| Q1 | C |
| Q2 | A |
| Q3 | B |
| Q4 | B |
| Q5 | B |
| Q6 | B |
| Q7 | C |
| Q8 | C |
| Q9 | A |
| Q10 | C |
🧠 Explanations
- Q1 → C: Immediate mode has operand inside instruction.
- Q2 → A: Memory address directly given → Direct addressing.
- Q3 → B: Register Indirect → Register stores address of operand.
- Q4 → B: Arrays need indexed addressing.
- Q5 → B: Relative addressing uses PC.
- Q6 → B: Convoy effect is part of scheduling (OS concept).
- Q7 → C: Both formulas can represent EA in different contexts.
- Q8 → C: Indirect needs 2 memory accesses (fetch address, then operand).
- Q9 → A: Register is fastest (no memory reference).
- Q10 → C:
(R2)means register indirect.
🎯 Why This Practice Matters for ECET 2026
Addressing modes are always asked in COA section (2–3 marks).
👉 Direct, Indirect, and Indexed are most common in ECET papers.
👉 Understanding formulas helps in solving numerical problems on Effective Address calculation.
👉 Also very useful in GATE & job interviews.
📲 Join Our ECET Prep Community
For daily MCQs, solved notes & video sessions:
👉 Join Our Telegram Community
