A Level Computer Science OCR Test 2025 – 400 Free Practice Questions to Pass the Exam

The Memory Data Register (MDR) serves a critical role in CPU operations by temporarily storing data that is either being loaded into the CPU from memory or written back to memory. When the CPU retrieves data from RAM for processing, that data is placed in the MDR so that the CPU can utilize it as needed. Similarly, when the CPU needs to save data back to memory, it passes that data through the MDR. This function is essential for maintaining an efficient flow of data between the CPU and memory, allowing for smooth execution of programs.

In contrast, other options refer to different registers or CPU functions. Holding the address of the next instruction pertains to the role of the Program Counter (PC), which tracks where the CPU is in its execution sequence. Preparing data for processing by the Arithmetic Logic Unit (ALU) involves other CPU operations but does not specifically relate to the role of the MDR. Finally, executing fetched instructions is a duty handled by the control unit and doesn't apply to the MDR's function. This understanding emphasizes how the MDR plays a fundamental part in the data management process within the CPU architecture.