Addressing Modes in Computer Architecture

Front

Immediate Addressing Mode

Back

Operand is directly in the instruction itself. No memory access needed to fetch operand. Example: MOV R1, #25 → Load the value 25 into register R1.

Front

Register Addressing Mode

Back

Operand is in a CPU register. Instruction specifies register name, not a memory address. Example: ADD R1, R2 → Add contents of R2 to R1.

Front

Direct Addressing Mode

Back

The instruction contains the actual memory address of the operand. Example: MOV R1, (5000) → Move contents of memory location 5000 into R1.

Front

Indirect Addressing Mode

Back

Instruction specifies a register or memory location that contains the address of the operand. Requires one extra memory fetch. Example: If R2 = 7000 and Memory[7000] = 50, MOV R1, (R2) → R1 gets 50.

Front

Indexed Addressing Mode

Back

Operand’s address = Base address + Index value. Useful for accessing arrays. Example: If R3 = base = 2000, X = index = 5, MOV R1, 5(R3) → Access memory location 2005.

Front

Base Register Addressing Mode

Back

Similar to indexed, but index value comes from a register rather than being fixed in the instruction. Example: Base register R4 + offset in instruction.

Front

Relative Addressing Mode

Back

Address = PC (Program Counter) + offset in instruction. Often used in branch instructions. Example: BEQ +20 → Branch if equal, 20 bytes ahead from current PC.

Front

Auto-increment / Auto-decrement Addressing

Back

Access the operand and then automatically increment or decrement the pointer register. Example: (R5)+ → Use value at address in R5, then R5 = R5 + 1.