CPU: Performance and Architecture

What is the main function of the CPU?

To carry out processing by fetching and executing instructions.

Where are instructions fetched from

From the main memory (RAM).

What does the ALU do?

Performs arithmetic operations (add, subtract) and logical comparisons.

What does the Control Unit (CU) do?

Sends control signals, manages instructions

What is a register?

A fast storage area in the CPU that holds instructions, data, or addresses, usually one value.

What is cache memory?

A fast, small storage area that stores frequently used instructions

What are the three stages of the Fetch–Decode–Execute cycle?

Fetch, Decode, Execute.

What happens during Fetch?

CU fetches the next instruction from main memory.

What happens during Decode?

The CU decodes the instruction and prepares components.

What happens during Execute?

The instruction is carried out, often using the ALU, and may involve memory read

What does the Program Counter (PC) do?

Holds the address of the next instruction.

What does the MAR do?

Stores the address of the instruction or data being used.

What does the MDR do?

Holds the instruction

What does the Accumulator (ACC) do?

Temporarily stores results of calculations.

What is Von Neumann architecture?

Stores programs and data in the same memory.

What is Harvard architecture?

Has separate memory for programs and data.

How does the CPU distinguish between instructions and data in Von Neumann?

By the stage of the fetch–execute cycle and whether the address came from the PC.

What does RAM store in Von Neumann architecture?

Currently running program instructions, the OS, and data in use (like open files).

What is the Von Neumann bottleneck?

Performance limitation from using the same memory and buses for instructions and data.

How do CPUs reduce the bottleneck?

Use cache and wider buses.

What are the three levels of cache?

L1: fastest, smallest (2–256KB, per core). L2: larger, slower (256KB–8MB, per core). L3: biggest, slowest (4–50MB, shared).

Why is cache faster than RAM?

It’s closer to the CPU and uses faster technology.

How does clock speed affect performance?

Higher speed = more instructions per second → faster CPU, but more heat

How do cores affect performance?

More cores allow more tasks to run simultaneously.

Can software always use multiple cores?

No, it depends if the software is designed for multi-core use.

What is an embedded system?

A computer built into another device for a specific function.

Give examples of embedded systems.

Washing machines, smartwatches, microwaves, traffic lights, GPS, cameras.

How do embedded systems differ from general-purpose computers?

General-purpose can run many programs; embedded systems only do one task.