When a CPU fetches an instruction word from memory, the word contains an operation code (op code) that indicates the type of operation the CPU is to perform and information specifying where the instruction operands are located. A computer may use various addressing modes to specify the operand location. One such addressing mode is shown below, where R designates some register within the CPU and d is a constant embedded in the instruction word
Which of the following terms best describes the addressing mode used by the instruction above?
A. Immediate addressing
B. Direct addressing
C. Indexed addressing
D. Indirect addressing
Addressing modes specify the method used to detail the operand of an instruction. The operand of an instruction is both the part that specifies the data that is to be operated on as well as the data itself. Let's define the four possible addressing modes we are choosing between:
Based on these explanations, the addressing type being shown in the problem is C, indexed addressing. As described above, R would be our index register and d would be our offset. The sum sign indicates the calculations needed to be performed to arrive at the operand address.