Direct Address Mode and Effective Address

In computer architecture, addressing modes define how the operand's location is specified in an instruction. The effective address is the final memory location or register where the operand is found.

Understanding Addressing Modes

The question asks for the addressing mode where the effective address is identical to the address specified in the instruction's address field.

• Implied Mode: The operand is implicitly defined by the instruction itself, often using a specific CPU register like the accumulator. The address part of the instruction is typically unused or irrelevant for locating the operand.
• Direct Address Mode: In this mode, the address field of the instruction directly contains the effective address of the operand in memory. No calculation or indirection is needed.
• Immediate Mode: The address field of the instruction contains the operand itself, not an address. This is used for constants. The concept of effective memory address doesn't apply here in the same way.
• Register Indirect Mode: The address field of the instruction specifies a register. The effective address is the value stored *inside* that register, which is the memory address of the operand.

Identifying the Correct Mode

Based on the definitions:

• Direct Address Mode fits the description perfectly: the effective address IS the address part of the instruction.
• Implied Mode doesn't use the address part for effective address calculation.
• Immediate Mode uses the address part as the data itself.
• Register Indirect Mode uses the *contents* of a register, not the address part directly.

Therefore, the addressing mode where the effective address is equal to the address part of the instruction is the Direct Address Mode.