Data Storage (Copy)
IGCSE / O Level Computer Science Cheat Sheet
Topic: 3.3 Data Storage
📥 Primary Storage (Main Memory)
Directly accessible by the CPU; used to store data and instructions currently in use.
| Type | Description | Volatile? | Use |
|---|---|---|---|
| RAM (Random Access Memory) | Temporary storage of active programs and data | ✅ | Holds programs currently running |
| ROM (Read Only Memory) | Stores fixed instructions like the BIOS | ❌ | Boot-up instructions (firmware) |
📤 Secondary Storage
Non-volatile storage for long-term data retention; not directly accessed by the CPU.
| Storage Type | Description | Examples |
|---|---|---|
| Magnetic | Uses spinning platters and magnetic fields | HDDs, magnetic tapes |
| Optical | Uses lasers to read/write pits on a disk surface | CDs, DVDs, Blu-ray discs |
| Solid-State | Uses NAND flash memory; no moving parts | SSDs, USB drives, SD cards |
⚙️ Storage Type Comparison
| Feature | Magnetic | Optical | Solid-State |
|---|---|---|---|
| Speed | Moderate | Slow | Fast |
| Durability | Prone to damage | Easily scratched | Very durable |
| Cost per GB | Low | Very low | Higher |
| Portability | Moderate | Good | Excellent |
| Typical Use | OS & large files | Media distribution | Laptops, phones |
🔁 Virtual Memory
- Extension of RAM using space on secondary storage
- Used when RAM is full
- Slower than real RAM
- Swaps pages between RAM and virtual memory
☁️ Cloud Storage
Stores data on remote servers, accessed via the internet.
| Advantage | Disadvantage |
|---|---|
| Access data anywhere | Needs stable internet connection |
| Off-site backup | Ongoing subscription costs |
| Share and sync easily | Privacy and security concerns |
| Saves local storage space | Relies on third-party service |