A Level Computer Science OCR Practice Exam

The Accumulator (ACC) plays a vital role during the execution phase of a CPU's operation. It is a specific register used to store intermediate results and hold data being processed. During the execution phase, the CPU performs arithmetic and logic operations, and the results of these operations are typically stored in the Accumulator. For example, when performing addition or other calculations, the operands are fetched, processed, and the result is stored back in the ACC, making it crucial for the CPU's ability to perform tasks sequentially. In contrast, the Memory Address Register (MAR) primarily deals with addressing memory locations rather than executing instructions. The Program Counter (PC) is responsible for keeping track of the next instruction to be executed, moving to the next instruction after fetching the current one. General-purpose registers also play a role in the execution but are not specifically tailored for this phase as the Accumulator is. Thus, the ACC is the most directly involved in the execution of calculations within the CPU.