GU1: 9. Registers & FDE

Registers: What are CPU registers?

Very small, very fast memory inside the CPU used during processing.

Registers: What does the Program Counter do?

Holds the address of the next instruction to be fetched.

Registers: What does the Memory Address Register (MAR) do?

Stores the address of the memory location the CPU wants to access.

Registers: What does the Memory Data Register (MDR) do?

Hold the data being transferred to/from memory.

Registers: What does the Current Instruction Register do?

Stores the instruction currently being decoded/executed.

Registers: What is the Accumulator?

Stores intermediate results from calculations

(working space for maths)

Fetch-Decode-Execute: What is the fetch-decode-execute cycle?

The process the CPU uses to run instructions.

Fetch-Decode-Execute: What happens in the fetch stage?

The program counter gives the address to the memory address register.

Memory sends instruction to MDR

Instruction moved to CIR

Program Counter increases by 1

Fetch-Decode-Execute: What happens in the decode stage?

Control Unit interprets the instruction

Figures out what needs to happen

Fetch-Decode-Execute: What happens in the execute stage?

CPU carries out the instruction

May involve ALU, memory, or I/O

Fetch-Decode-Execute: What is the ALU?

Arithmetic Logic Unit

Fetch-Decode-Execute: What does the ALU do?

Performs calculations and logic operations