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Secondary storage retains data beyond a running process. Compare mechanisms, access patterns and durability rather than treating capacity or price as a permanent universal ranking.
What you'll be able to do
A hard disk records magnetic states on rotating platters, using moving read/write heads to access tracks and sectors. Mechanical movement contributes seek and rotational delay, while sequential transfer can amortise those costs over a large contiguous read.
Optical media use a laser and reflected-light differences to read encoded patterns. Writable and rewritable technologies use different recording materials, so not every optical disc is written by the same mechanism. Media compatibility, capacity, handling and access speed affect whether a format suits distribution or storage.
An SSD commonly uses NAND flash cells that retain charge in a floating-gate or charge-trap transistor structure without continuous power. Data are organised into pages within larger erase blocks. Programming and erasing have constraints: rewriting data can require writing a new page and later erasing a whole block rather than simply overwriting any byte in place.
The controller manages address mapping, wear levelling and housekeeping such as garbage collection. No moving head gives low access latency relative to mechanical seeks, but writes, endurance and controller behaviour still matter. “No moving parts” is not a guarantee of infinite life or immunity to every fault.
Secondary storage is non-volatile under normal conditions, unlike ordinary working RAM. Access latency, sustained transfer rate, capacity, endurance, portability, energy and cost are different criteria. A backup also needs an appropriate retention and recovery process, not merely an extra large device.
Choose evidence relevant to the workload: random database reads differ from sequential archival transfer. Prices and capacities change, so avoid teaching one permanent product ranking as a law. Physical deletion of a filename also need not immediately erase every underlying stored copy; storage mechanisms and management policies affect the result.
| Medium | Mechanism | Important consideration |
|---|---|---|
| Magnetic disk | Magnetic recording with moving parts | Seek/rotation affect random access |
| Optical disc | Laser reads optical differences | Drive/media compatibility |
| SSD | Flash cells plus controller | Page writes, block erasure and endurance |
Attempt the task before opening its worked response. Record each change of state, explain the rule used, and check the result against the original requirements. Code examples labelled Python 3 use that language’s conventions; pseudocode states its own assumptions.
Common mistakes to avoid
Key takeaways
Test yourself
Answer a few questions, then review anything you missed.
Start with the quiz above to check the key ideas. You can also choose another topic from the practice library.