Computer Science (2210)
ALU (Arithmetic Logic Unit): Does calculations and logic comparisons CU (Control Unit): Fetches, decodes, and executes instructions Registers: Tiny, super-fast memory inside the CPU
FETCH: Get the next instruction from RAM DECODE: Work out what the instruction means EXECUTE: Carry out the instruction
RAM (Random Access Memory): Temporary, volatile (lost when power off). Stores running programs. ROM (Read Only Memory): Permanent, non-volatile. Stores BIOS/startup instructions. Cache: Very fast, small memory between CPU and RAM
HDD: Magnetic, cheap, large capacity, slow (spinning disk) SSD: Flash memory, fast, more expensive, no moving parts Optical: CD, DVD, Blu-ray (laser reads/writes) USB Flash: Portable, solid state
Input: Keyboard, mouse, microphone, camera, scanner, touchscreen Output: Monitor, printer, speaker, projector
Topic 2 of 5Cambridge O Levels
Computer Hardware
Components inside a computer and how they work together
A computer system has input, processing, storage, and output components.
The CPU (Central Processing Unit):
The "brain" of the computer. Has three main parts:
The Fetch-Decode-Execute Cycle:
This happens billions of times per second!
Memory Types:
Storage Devices:
Input & Output Devices:
Key Points to Remember
- 1CPU = ALU + Control Unit + Registers
- 2Fetch-Decode-Execute cycle runs billions of times per second
- 3RAM = volatile (temporary), ROM = non-volatile (permanent)
- 4SSD is faster but more expensive than HDD
Pakistan Example
Hafeez Centre Lahore — Pakistan's Tech Hub
Walk into Hafeez Centre in Lahore and you'll find every computer component discussed in this chapter. Vendors sell RAM sticks (4GB, 8GB, 16GB — more RAM means more programs can run simultaneously). SSDs are taking over HDDs because they're faster (no spinning disk). A budget gaming PC might have: Intel i5 CPU (4 cores, 3.5 GHz clock speed — that's 3.5 billion fetch-decode-execute cycles per second!), 16GB RAM, 512GB SSD, and a dedicated GPU. The shopkeeper who can explain these specs knows his computer architecture!