AQA A-level: Structure and role of the processor and its components

This is a set of flashcards that explain what each component in the processor does

Arithmetic and Logic Unit (ALU)

Performs all logical and numerical calculations

Clock

Provides the timing signal used to synchronise processor and all other components and the movement of data across other components

General purpose registers

A series of small memory locations on the processor available for different uses

Memory address register (MAR)

Holds the address to be put on the address bus

Control unit

• It runs the fetch execute cycle

• Synchronises and controls all other components

• Contains instruction decoder to decode instructions

Memory data register (MDR) or Memory buffer register (MBR)

Holds the data that was taken from the data bus OR it holds the data to be put on the data bus

Program Counter (PC)

Holds the address of the next instruction

Current instruction register (CIR)

Holds the current instruction

Interrupt register

Holds interrupt

Status register (and when it’s contents are updated)

Provides information about the result of the last (arithmetic/logical) instruction.

Contents updated when:

• When the result of a comparison / (arithmetic) operation is zero/negative

• When a carry needs to be carried out; When overflow/underflow occurs

• When an interrupt occurs

• When a comparison is made a flag is set as to whether the operands were equal;