Optical, Magnetic, Solid State

Common types of storage: Optical, Magnetic, Solid State

1.2.2 Secondary Storage

Secondary Storage — Note 2 of 4

What you need to know

There are three main types of secondary storage: solid-state (SSDs, flash drives), optical (CDs, DVDs, Blu-rays), and magnetic (hard disk drives). Each has different characteristics that make it suitable for different applications.

What to know

All three types are non-volatile: they keep data when the power is turned off, which is why they are used for long-term storage.
How data is stored: solid-state traps electrical charge in memory cells (flash memory); optical uses a laser to read pits and lands on the surface of a disc; magnetic uses a read/write head to magnetise tiny regions of a spinning platter.
Moving parts: an HDD has a spinning platter and a moving head, so it takes longer to find data and can be damaged if dropped. SSDs have no moving parts, so they are faster, silent and more resistant to knocks.
Speed (fastest first): solid-state, then magnetic, then optical.
Capacity: HDDs and SSDs can store several terabytes; optical discs hold far less (CD about 700 MB, DVD about 4.7 GB, Blu-ray 25 to 50 GB).
Cost: magnetic is the cheapest per GB for large amounts of data; optical discs are cheap to make individually; solid-state is the most expensive per GB.
Portability: SSDs, USB flash drives and optical discs are small and light; HDDs are bulkier and heavier.
Reliability: each type can fail for a different reason: HDDs through mechanical wear, optical discs through scratches, SSDs after a limited number of write cycles.

Key terms

Solid-State Storage: Uses electrical circuits with no moving parts (e.g. SSDs, USB flash drives). Very fast and durable.
no moving parts, fast read/write, lightweight, durable, but expensive per GB.
Optical Storage: Uses a laser to read/write data on discs (e.g. CDs, DVDs, Blu-rays). Cheap per disc but low capacity.
very cheap per disc, small and lightweight, but low capacity and easily scratched.
Magnetic Storage: Uses magnetised regions on spinning platters (e.g. HDDs). High capacity and cheap per GB, but has moving parts.
high capacity, cheap per GB, but bulky, fragile (moving parts), and slower than SSDs.

Exam technique

Tip:When comparing storage types, always relate to the SPECIFIC CHARACTERISTICS asked about (capacity, speed, portability, durability, reliability, cost).
Tip:For cost, say 'cheaper per GB' or 'cheaper cost per unit of data' — NOT just 'it is cheap to buy'.
Mistake:Saying SSDs have 'unlimited lifespan' or 'more longevity than magnetic'. SSDs have a limited number of write cycles.
Tip:Six characteristics to consider: capacity, speed, portability, durability, reliability, cost.

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Practise 1.2.2 questions

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