Computer Science A1.1.1 Simple

CPU

Executes program instructions.

ALU

Performs arithmetic and logical operations.

CU

Decodes instructions and sends control signals to other CPU components.

Register

A small, very fast storage location inside the CPU.

PC

Holds the memory address of the next instruction to be fetched.

IR

Holds the instruction currently being decoded and executed.

MAR

Holds the address of the memory location currently being accessed.

MDR

Holds data or an instruction being transferred between memory and the CPU.

AC

Holds intermediate results produced by the ALU.

PC vs MAR

PC holds the address of the next instruction; MAR holds the address currently being accessed in memory.

IR vs MDR

IR holds the current instruction; MDR holds data or instructions being transferred to or from memory.

Address bus

Carries memory addresses from the CPU to memory. It is one-directional.

Data bus

Carries data and instructions between the CPU and memory. It is bi-directional.

Control bus

Carries control and timing signals between the CPU and other components.

Fetch order

PC → MAR → RAM → MDR → IR.

Single-core

A processor with one processing core.

Multi-core

A processor with multiple cores that can process instruction streams in parallel.

Co-processor

A specialised processor that assists the main CPU with specific tasks.

Why is multi-core not always much faster?

Extra cores only help when the workload can be divided into tasks that run in parallel.