In CPU organization, what is the correct role of the Memory Buffer Register (MBR) during memory read and write operations?

Introduction / Context:
The CPU communicates with memory through well-defined registers. Two key registers are the Memory Address Register (MAR) and the Memory Buffer Register (MBR, also called MDR for Memory Data Register). Understanding their distinct roles clarifies the fetch–decode–execute cycle and bus transactions.

Given Data / Assumptions:

• We distinguish between address and data stages of a memory operation.
• Standard naming: MAR holds addresses; MBR/MDR holds data.
• MBR temporarily buffers data across the CPU–memory interface.

Concept / Approach:

During a read: the CPU places the target address in MAR, asserts a read signal; memory returns the requested word into the MBR, from which the CPU consumes it. During a write: the CPU places the destination address in MAR and the outbound data in MBR, then asserts write; memory stores the MBR's content at the addressed location.

Step-by-Step Solution:

Verification / Alternative check:

Architecture texts consistently define MAR/MBR (or MDR) with these responsibilities, matching bus protocol timing diagrams.

Why Other Options Are Wrong:

• current instruction location: that is the Program Counter (PC).
• hardware circuits that perform instructions: describes the Control Unit/ALU, not MBR.
• contains the address: that is MAR.

Common Pitfalls:

• Confusing MBR with MAR due to similar naming or MDR aliasing.

Final Answer:

contains the data read from the memory location (after a read) or the data to be written (before a write).