Principles of Computer System Operation 🖥️
What's actually inside the box: hardware components, how the CPU runs instructions, the devices you talk to it through, and where it remembers things.
🎯 What you'll unlock this lesson
- ✅ Identify the components of a computer system and what each one does
- ✅ Explain the fetch–decode–execute cycle
- ✅ Classify devices as input, output, or both
- ✅ Distinguish memory (RAM) from storage
🧩 The five components 4.1
📥 Input
Gets data into the system — keyboard, mouse, microphone, camera...
🧠 Processing
The CPU — carries out instructions and calculations.
🗄️ Memory
RAM — holds data and instructions the CPU is using right now.
💽 Storage
Keeps data long-term, even with the power off.
📤 Output
Gets results out of the system — monitor, printer, speaker...
This applies to desktops, laptops, tablets, smartphones, and servers alike — every one of them has all five, just packaged differently. Their operating systems differ too: Windows and macOS on desktops/laptops, Android and iOS on phones/tablets, Linux commonly on servers.
🃏 Key-term flashcards tap to flip
⚙️ Inside the CPU 4.2
ALU
Arithmetic Logic Unit — does the actual maths and comparisons.
Control Unit
Directs the fetch–decode–execute cycle and coordinates the other parts.
Registers
Tiny, extremely fast storage slots inside the CPU that hold values mid-calculation.
🎮 Interactive Fetch–Decode–Execute Visualizer signature move
Every single instruction a CPU runs goes through the same 3-stage cycle, over and over, billions of times a second. Step through it running Result ← 3 + 4.
🔢 Data representation
Whatever kind of data goes in — text, numbers, audio, images, or video — the CPU only ever works with one thing: binary. Everything gets encoded into bit patterns before it's processed, and decoded back into something people recognise on the way out.
| Data type | Everyday example |
|---|---|
| Text/string | A message, a filename |
| Number | A score, a temperature reading |
| Audio | A voice recording, a song |
| Image | A photo, an icon |
| Video | A movie clip, a security-camera feed |
🎛️ Input/Output devices 4.2.2
Click a device to see what category it belongs in.
🌾 Activity 4.1 — sensors & IoT
- 1️⃣ What CPU type is in the device you're using right now?
- 2️⃣ List the sensors in a smartphone and what each one is for (e.g. accelerometer, fingerprint, GPS).
- 3️⃣ Give an example of another everyday device that uses a sensor.
- 4️⃣ Brainstorm an IoT application that could help your own family day-to-day — a smart-irrigation system for a home garden, for example.
💾 Memory vs. storage 4.2.3
🗄️ RAM (Memory)
- ⚡ Volatile — cleared when the power turns off
- 🏎️ Very fast — holds what the CPU is using right now
- 🔬 Built from DRAM technology
💽 Secondary storage
- 💾 Non-volatile — keeps data with the power off
- 🐢 Slower than RAM, but much larger capacity
- 📁 Where files live long-term
Common file types
Executable, text, document, spreadsheet, audio, image, and video files — each stored as its own pattern of bytes, and each worth backing up since storage devices can fail.
The full breakdown of secondary-storage device types (HDD, SSD, optical discs, memory cards) and all of §4.3 Application Software were on pages missing from the scan. These will be added once that material is available, rather than guessed at here.