Learn: What Registers Do (Big Picture)

Welcome!Building on what you've already learned about the CPU and the fetch–decode–execute cycle, we're now going to explore the important role of registers in the CPU. Registers are key to how instructions are processed efficiently.

What Are Registers?Registers are small, fast storage locations inside the CPU. They temporarily hold data and instructions during processing. These are much faster than RAM, ensuring the CPU operates efficiently.

Why Are Registers Important?Registers are critical because they store key information required for each step of the fetch–decode–execute cycle. Without registers, the CPU would need to access slower memory like RAM repeatedly, making processing inefficient.

Key Registers in Von Neumann ArchitectureVon Neumann architecture uses specific registers for instruction processing:Program Counter (PC): Stores the address of the next instruction to be executed.Memory Address Register (MAR): Holds the address of the memory location to be accessed.Memory Data Register (MDR): Temporarily stores data fetched from or written to memory.Accumulator (ACC): Holds intermediate results of calculations performed by the CPU.

Memory Address Register (MAR)The MAR is used to store the memory location (address) that the CPU needs to access. For example, during the fetch stage, the MAR holds the address of the instruction to be retrieved from memory.

Memory Data Register (MDR)The MDR temporarily stores the data being transferred to or from memory. This ensures the CPU has immediate access to the data it needs for processing.

Accumulator (ACC)The Accumulator is a special register that stores results of calculations performed by the Arithmetic Logic Unit (ALU). For example, if the CPU adds two numbers, the result will be stored in the accumulator before being written to memory.

Review Time!Great work! You've learned about the key registers in the CPU and their roles in processing instructions. Let's test your understanding with a few review questions.