A Level Computer Science OCR Practice Exam

The correct choice relates to the component of the CPU that temporarily holds data during processing. The Memory Data Register (MDR) serves this key role; it is specifically designed to hold the data that is being transferred to or from the memory during the execution of instructions. This includes both instructions and the data needed by those instructions.

When a CPU fetches an instruction from memory, that instruction is first placed in the Memory Data Register before it is sent to the control unit for decoding and execution. This process allows the CPU to manage data flow efficiently and ensures that the instructions are ready to be processed in a timely manner.

In contrast, other components such as the Memory Address Register (MAR) are involved in addressing memory locations, while the Program Counter (PC) keeps track of the next instruction to be executed. Registers are small, fast storage locations within the CPU used for various operations but do not specifically hold instructions prior to processing. Understanding the specific functions of these components clarifies why the Memory Data Register is the vital component for temporarily holding data and instructions just prior to processing.