Which register holds the data fetched from memory or to be written to memory?

• A. Memory Address Register
• B. Arithmetic Logic Unit
• C. Memory Data Register
• D. Cache

Answer: (C)

The main idea is that there is a dedicated data buffer between the CPU and memory. The register that holds the data being transferred to or from memory is the Memory Data Register. When the CPU fetches something from memory, the address to access is placed in the Memory Address Register, memory retrieves the data and places it into the Memory Data Register so the CPU can use it. For writes, the value to be stored goes into the Memory Data Register, and the memory uses the address in the Memory Address Register to perform the write.

The Arithmetic Logic Unit isn’t used to hold memory data; it performs computations. Cache isn’t the single register used in the transfer; it’s a fast storage layer that holds copies of memory blocks to speed up access, not the immediate buffer for a single fetch or write operation.