Solution

The correct answer is Index Addressing Mode.

Key Points

• The instruction LD ADR(X) which is equivalent to AC ← M[ADR + XR] is using the Index Addressing Mode.
• In Index Addressing Mode, the effective address of the operand is generated by adding a constant value (ADR) to the contents of an index register (XR).
• This mode is particularly useful for accessing array elements and iterating through data structures.

Additional Information

• Direct Addressing Mode: The operand's address is given explicitly within the instruction. For example, LD 500 means load the content of memory location 500 into the AC.
• Indirect Addressing Mode: The address field of the instruction points to a memory location that contains the effective address of the operand. For example, LD (500) means load the content of the memory location whose address is stored in memory location 500.
• Immediate Addressing Mode: The operand is specified within the instruction itself. For example, LD #10 means load the value 10 directly into the AC.