Addressing Modes in Computer Architecture



The addressing mode in computer architecture refers to the way in which the operands of an instruction are specified. It determines how the CPU accesses data or operands from memory or registers. One common addressing mode is the immediate mode, which is the focus of this question.

Immediate Mode Addressing



Immediate mode addressing is an addressing mode in which the operand is specified as a constant value within the instruction itself. The constant is typically specified after the opcode byte, making it a part of the instruction.

Explanation of the Options



Let's go through each option to understand why immediate mode is the correct answer:

a) Register Instructions:
In register instructions, the operands are specified using registers. The instructions operate on the values stored in the registers, and no constants are involved. Therefore, immediate mode is not applicable here.

b) Register Specific Instructions:
Similarly to register instructions, register-specific instructions also operate on registers without involving any constants. Hence, immediate mode is not applicable in this case either.

c) Direct Addressing:
Direct addressing involves specifying the memory address where the operand is stored. It does not directly involve specifying a constant value within the instruction. Therefore, immediate mode is not applicable here.

d) Immediate Mode:
Immediate mode is the correct answer as it specifically involves specifying a constant value within the instruction itself. The constant is usually specified after the opcode byte, making it a part of the instruction.

Conclusion



In immediate mode addressing, a constant is specified in the instruction itself, typically after the opcode byte. This allows the CPU to directly access and use the constant value as an operand for the instruction. Immediate mode is different from other addressing modes like register instructions, register-specific instructions, and direct addressing, which do not involve specifying a constant value in the instruction.