Cambridge IGCSE Computer Science · Syllabus 0478 · Hardware
Memory Address Register
What is Memory Address Register?
The CPU register that stores the address of the memory location currently being accessed, and supplies that address to memory along the address bus; it never holds the data found at that address.
This definition is part of the Hardware chapter in Cambridge IGCSE Computer Science.
Common mistakes with Memory Address Register
- 3. “The MAR stores the instruction.” Why wrong The clue is in the name: memory address register. It holds a where, never a what. Correct model The MAR holds the address of the memory location currently being accessed, and supplies it to memory on the address bus. The instruction that comes back arrives in the MDR. Exam-safe “The MAR stores the address of the memory location currently being accessed.” Check: during the fetch of the instruction at address 100, what is in the MAR?100 — the address, not the instruction stored there.