Structure and role of the processor and its components

major components in the CPU

- arithmetic logic unit

- control unit

- registers

- clock

ALU

performs arithmetic and logic operations (maths, boolean operations)

Control unit

controls various components of the processor by sending signals and decodes instructions

Clock

- generates a timing signal at a regular frequency to synchronise communication between components and processor and rest of computer system

Registers

- program counter

- current instruction register

- memory address register

- memory data register

- status register

program counter

holds memory address of next instruction (increments after each cycle)

current instruction register

holds instruction currently being executed by the processor

memory address register

stores the address of a memory location that is to be read or written to

memory data register

holds contents of memory location that has been read from or data that is to be stored

status register

holds current state of processor

fetch

1. contents of PC copied to MAR

2. MAR gets instruction from main memory through address bus

3. data at memory location is sent into MDR by data bus

4. program counter increments

5. contents of MDR copied into CIR

decode

- contents of CIR decoded by control unit

- decoded instruction split into opcode and operands

opcode

- specificies the operation

operand

- data for the operation

execute

instruction carried out

1. required data is fetched

2. instruction is carried out

3. results stored in general purpose registers or main memory

processor instruction set

specifc group of instructions carried out by the processor (stored in machine code, with operands and opcode

addressing modes

immediate addressing

direct addressing

immediate addressing

operand is datum

direct addressing

operand is address of datum

factors affecting processor performance

- number of cores

- cache memory

- clock speed

- word length

- address bus width

- data bus width