CS P1 - 1.1.1 - Structure and function of the processor

What are the components of the CPU and describe them?

CU, ALU, registers

CU - Control Unit: the circuit coordinating the activities of a processor

ALU - Arithmetic Logic Unit: the circuit that performs the mathematical and boolean operations on the data

Registers: small, quick stores of data within the processor

What are the registers used in the FDE cycle?

- PC: Program Counter, holds the address of the next instruction to be executed

- MAR: Memory Address Register, holds the address of the instruction/data being fetched or written to

- MDR: Memory Data Register, holds the instruction/data being fetched or written to

- CIR: Current Instruction Register, holds the instruction being executed right now

- ACC: Accumulator, holds the result from the instruction

What is a bus, and the different types?

It is a collection of parallel wires through which data is transmitted. Unidirectional - one way, Bidirectional - 2 way.

Address Bus: sends a memory address from the CPU to the memory (unidirectional)

Data Bus: sends the actual data or instruction to and from the memory (bidirectional)

Control Bus: carries commands from the CPU to other devices, and status messages back and from other devices (bidirectional)

What is in the Control Bus?

Messages are sent down this bus as a 1.

Read and Write signal - tell RAM to retrieve or store something

Clock - sends a consistent pulse to make sure everything is synchronised

Interrupt - fairly urgent task to tell the CPU to stop what it is doing.

What happens in Fetch of the FDE cycle?

tbc