iGCSE Computer Science - Distance Learning

Tutor Marked Assignment 6
Tutor Marked Assignment 8 (Programming)

The CPU Components & Registers

The majority of devices that we use today, will use the Von Neumann Architecture to run the Fetch Decode Execute Cycle that allows the processor to run instructions. The Von Neumann Architecture is often referred to as the Stored Program Concept – what this means is that both the instructions and the data are stored in the same format… binary

CPU registers are specific pieces of memory within the processor that hold memory to allow instructions to be fetched, decoded, and executed.

  • PC (Program Counter)
    • Holds the address of the next instruction to be processed
    • This is passed to the MAR
  • MAR (Memory Address Register)
    • Holds the address of the instruction to be processed
  • MDR (Memory Data Register – aka Memory Buffer Register)
    • Initially holds the instruction found at the address in the MAR
    • Then later, is used to store any data needed for the instruction
  • CIR (Current Instruction Register)
    • Holds the address currently being processed
  • Accumulator
    • Holds the outcome of the instruction
    • Can act like a running total in a calculator as more instructions are processed

Revision Task

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