What is the MDR?

• A. Memory Address Register
• B. Arithmetic Logic Unit
• C. Memory Data Register - holds the data fetched from or to be written to memory
• D. Cache

Answer: (C)

The Memory Data Register is the CPU register that holds data being transferred to or from memory. It acts as the temporary storage for the data that memory will read or write. When the CPU reads from memory, the requested word is placed into the Memory Data Register so the CPU can use it (for example, to load an operand into the accumulator or another register). When the CPU writes to memory, the data to be written is placed into the Memory Data Register and then written to the addressed location in memory. This register serves as the data path buffer between the CPU and memory and is distinct from the Memory Address Register (which holds the address) and from the ALU or cache.