The motherboard is the main circuit board that physically connects and allows communication between all other hardware components.
- CPU (Central Processing Unit)
- The 'brain' of the computer — fetches, decodes and executes instructions.
- ALU (Arithmetic Logic Unit)
- The part of the CPU that performs mathematical calculations and logical comparisons (e.g. >, <, =).
- CU (Control Unit)
- The part of the CPU that directs the operation of the processor — tells other parts what to do and when.
- Registers
- Extremely small, extremely fast storage locations built directly into the CPU, used to hold data currently being processed.
Primary storage holds data and instructions the CPU is actively using or needs immediate access to:
| Type | Volatile? | Purpose |
|---|
| RAM (Random Access Memory) | Yes — cleared when powered off | Temporarily holds running programs and their data |
| ROM (Read-Only Memory) | No — permanent | Stores essential start-up instructions that can't easily be changed |
| BIOS (Basic Input/Output System) | No — stored on a ROM/flash chip | The first software that runs on start-up; initialises hardware and hands control to the OS |
Secondary storage holds data permanently, even without power:
- Mechanical hard drive (HDD) — uses spinning magnetic platters; cheap per GB, slower, has moving parts.
- Solid state drive (SSD) — uses flash memory chips, no moving parts; faster and more durable, more expensive per GB.
- Hybrid drive — combines HDD (large capacity) with a small SSD cache (speed).
- Flash drives / SD cards — small, portable, solid-state storage.
- Optical storage — CDs/DVDs/Blu-ray discs, read with a laser.
Input devices bring data into the system:
- Pointing devices — mouse, trackpad, trackball, stylus.
- Keyboard types — standard, ergonomic, mechanical, virtual/on-screen.
- Scanners — convert physical documents/images into digital form.
- Microphones — capture sound.
- Biometric devices — fingerprint/face/iris scanners, used for identification.
- Sensors — e.g. an accelerometer detects motion/orientation (used in phones for screen rotation, in fitness trackers to count steps).
Output devices present the processed information to the user: monitors (visual), printers (physical copy), speakers/headphones (audio).
Ports are the physical connectors used to attach peripherals:
- USB (Universal Serial Bus) — the standard for connecting almost any peripheral (keyboard, mouse, flash drive, printer).
- HDMI (High-Definition Multimedia Interface) — carries both high-definition video and audio over a single cable, typically to a monitor or TV.
💡 Exam Tip
A common mark-losing mistake: calling RAM 'secondary storage'. RAM is primary storage and is volatile — always pair the term with whether it survives a power-off.