Question

Match the following with respect to connections between processor and memory.

Codes:

• A. a - iii, b - iv, c - ii, d - i
• B. a - i, b - ii, c - iv, d - iii
• C. a - ii, b - iv, c - iii, d - i
• D. a - iv, b - ii, c - i, d - iii

Hint:

Remember the keywords: MAR = Address, MDR = Data, IR = Instruction, and PC = Program execution tracking. The register names themselves often reveal their primary function.

Answer 1

The Correct Option is C

Step 1: Match IR (Instruction Register). The Instruction Register stores the instruction currently being decoded or executed by the CPU. During instruction execution:
• The instruction is fetched from memory.
• It is loaded into IR.
• The Control Unit decodes it.
• Execution begins. Therefore, \[ \text{IR} \rightarrow \text{Holds the instruction currently being executed} \] Hence, \[ (a) \rightarrow (ii) \]

Step 2: Match MAR (Memory Address Register). The Memory Address Register stores the address of the memory location that the CPU wants to access. Whenever data must be read or written:
• The address is first loaded into MAR.
• The address is transmitted through the address bus. Therefore, \[ \text{MAR} \rightarrow \text{Holds the address of the location to be accessed} \] Hence, \[ (b) \rightarrow (iv) \]

Step 3: Match MDR (Memory Data Register). The Memory Data Register temporarily stores data being transferred between memory and CPU. It may contain:
• Data read from memory.
• Data waiting to be written to memory. Therefore, \[ \text{MDR} \rightarrow \text{Data to be written into or read out of memory} \] Hence, \[ (c) \rightarrow (iii) \]

Step 4: Match PC (Program Counter). The Program Counter keeps track of the execution sequence of a program. It stores:
• The address of the next instruction to be fetched.
• The progression of program execution. Therefore, \[ \text{PC} \rightarrow \text{Keeps track of execution of a program} \] Hence, \[ (d) \rightarrow (i) \]

Step 5: Construct the final matching. {lcl} (a) IR & $\rightarrow$ & (ii)
(b) MAR & $\rightarrow$ & (iv)
(c) MDR & $\rightarrow$ & (iii)
(d) PC & $\rightarrow$ & (i) Conclusion: The correct matching is: \[ {\text{a - ii,\; b - iv,\; c - iii,\; d - i}} \] Hence, the correct answer is Option (C).