What is the MAR?

• A. Memory Data Register
• B. Macro Address Register
• C. Memory Allocation Register
• D. Memory Address Register - holds the address of where data or instructions will be fetched from or stored.

Answer: (D)

In CPU design, the Memory Address Register holds the address of the memory location to read from or write to. During a memory access, the CPU places the calculated or/and next-address into this register, and that value is driven onto the memory address bus so the memory unit knows which location to access. The actual data transferred to or from memory moves through a separate register, the Memory Data Register, which is why the MAR and MDR work together but serve different roles: MAR specifies where to access, while MDR carries the data being read or written. The other options aren’t standard terms for this role. Memory Data Register is the register that holds the data, not the address, and the other two options don’t correspond to common CPU components.