Secondary Storage Technologies
1. Magnetic Storage (HDD)
Hard Disk Drive (HDD)
Uses magnetized platters that spin at high speeds. A read/write head moves across the surface to change or read magnetic polarity.
Mechanism: Data is stored in concentric tracks and sectors. The polarity of the magnetic particles represents binary 1 or 0.
- Pros: High capacity, low cost per GB.
- Cons: Fragile (moving parts), slower access times (latency).
2. Optical Storage (CD, DVD, Blu-ray)
Optical Media
Uses a laser beam to read and write data on a reflective surface.
Mechanism: The laser burns "pits" into the surface. The areas between pits are "lands". The transition between a pit and a land represents a binary change.
- Pros: Portable, very cheap for distribution.
- Cons: Low capacity, slow read/write speeds, easily scratched.
3. Solid State Storage (SSD)
Solid State Drive (SSD)
Uses NAND Flash Memory. It has no moving parts and relies on electronic circuits.
Mechanism: Uses Floating Gate Transistors to trap electrons. If electrons are trapped in the "pool," it represents a 0; if empty, it represents a 1.
- Pros: Extremely fast, durable (no moving parts), silent.
- Cons: More expensive per GB, limited number of write cycles.
4. Summary Comparison
| Feature | HDD | SSD | Optical |
|---|---|---|---|
| Speed | Medium | Very High | Slow |
| Durability | Low (Physical shock) | High | Medium |
| Cost | Cheap | Expensive | Very Cheap |
| Capacity | Very High (1-18 TB) | High (Up to 8 TB) | Low (700MB - 100GB) |
⚠️ AS-Level Focus: Latency
In an HDD, Latency is the time taken for the specific sector to rotate under the read/write head. SSDs have zero rotational latency because they don't spin, which is why they feel so much faster when opening apps!