Describe the operation of magnetic, optical and solid-state storage with examples
📀 Data Storage: Magnetic, Optical & Solid‑State
💾 Magnetic Storage
Think of a magnetic storage device as a magnetic diary. The surface of the disk is coated with tiny magnetic particles that can be flipped to represent 0s and 1s. When the read/write head passes over the disk, it magnetises these particles to store data or detects their orientation to read data.
- Hard Disk Drives (HDDs) – the most common magnetic storage in PCs.
- Floppy Disks – old‑school, 1.44 MB capacity.
- Magnetic Tape – used for backups; long, thin tape rolls.
Key Features
- High capacity: up to several terabytes.
- Relatively slow access speed (seek time).
- Durable if kept away from magnets and shocks.
Exam Tips
Remember: Magnetic storage uses rotating disks and a read/write head. It is sequential – data is read in order, which can slow random access.
📀 Optical Storage
Optical media store data as tiny pits and lands on a disc surface. A laser beam reads the pattern: pits reflect light differently to the laser than lands. Think of it as a laser‑etched diary.
- CDs – 700 MB, 1.2 GB per disc.
- DVDs – 4.7 GB (single layer) or 8.5 GB (dual layer).
- Blu‑ray – 25 GB (single layer) or 50 GB (dual layer).
Key Features
- No moving parts inside the disc; only the drive head moves.
- Read speed depends on laser wavelength.
- Good for long‑term archival; less susceptible to magnetic fields.
Exam Tips
Key point: Data is stored as pits and lands read by a laser. The laser wavelength determines the disc’s capacity.
💾 Solid‑State Storage (SSD)
Solid‑state devices use flash memory – tiny transistors that can be turned on or off to store bits. Imagine a digital notebook where each page is a memory cell that can be written to instantly.
- USB flash drives – portable, 4 GB–128 GB.
- SSD internal drives – 250 GB–4 TB, used in laptops.
- eMMC & UFS – built into phones and tablets.
Key Features
- Very fast random access (latency < 0.1 ms).
- No moving parts – more shock‑resistant.
- Lower capacity per unit cost compared to HDDs.
Exam Tips
Remember: SSDs use flash memory cells that can be written and read instantly. They are non‑volatile and durable but have a limited number of write cycles.
📊 Storage Comparison
| Type | Example | Capacity | Speed | Durability | Cost |
|---|---|---|---|---|---|
| Magnetic | HDD | 1–10 TB | ~200 MB/s | Good if protected from shocks | Low |
| Optical | Blu‑ray | 25–50 GB | ~20 MB/s | Very good | Medium |
| Solid‑State | SSD | 250 GB–4 TB | ~500–550 MB/s | Excellent (no moving parts) | Higher |
📝 Final Exam Tip
When comparing storage types, always consider capacity, speed, durability, and cost. Use the mnemonic “CSDC” (Capacity, Speed, Durability, Cost) to remember the key factors.
Revision
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