Learn: What Registers Do (Big Picture)

Welcome!Welcome back! You've already learned about why the CPU is essential and how the fetch-decode-execute cycle works. Today, let’s dive deeper into the role of registers and how they help keep everything running smoothly in the CPU.

What Are Registers?Registers are small, fast storage locations inside the CPU. They temporarily hold data or instructions that the CPU is actively working with. Registers are essential for improving the speed of processing by keeping frequently used data close to the CPU.

Key Registers in the CPUThe CPU contains several key registers, each with a specific role. Let’s explore the most important ones you need to know for your OCR GCSE:

Program Counter (PC)The Program Counter stores the memory address of the next instruction to be executed. Once the CPU fetches this instruction, the PC is updated to point to the next instruction in the sequence.

Memory Address Register (MAR)The Memory Address Register (MAR) holds the memory address of the data or instruction that the CPU needs to access from memory. It acts as a pointer to the required data or instruction.

Memory Data Register (MDR)The Memory Data Register (MDR) temporarily holds the actual data or instruction fetched from memory. It works closely with the MAR to ensure the CPU processes the correct information.

Accumulator (ACC)The Accumulator is a register that stores intermediate results of calculations performed by the Arithmetic Logic Unit (ALU). This makes it faster for the CPU to work on a sequence of calculations.

How Do Registers Work Together?During the fetch-decode-execute cycle, the registers work as a team. For example, the PC provides the address of the next instruction, the MAR points to the location in memory, the MDR holds the fetched data, and the ACC stores calculation results. This coordinated effort ensures the CPU runs efficiently.

Review Time!Great work! You’ve learned how registers like the PC, MAR, MDR, and ACC work together during processing. Let’s test your understanding with a few final questions!

Congratulations!You’ve successfully learned about the key registers in the CPU and how they work together to process instructions. Keep practising to reinforce your understanding!