Understand the need for secondary storage and compare the three types: magnetic, optical and solid state.

What this dot point is asking

AQA wants you to explain why secondary storage is needed and to compare the three types (magnetic, optical and solid state) by their characteristics and typical uses.

Why secondary storage is needed

When choosing storage, the key characteristics to compare are capacity (how much it holds), speed (how fast it reads and writes), portability (whether it is easily moved), durability (how well it survives knocks), and cost per gigabyte. Different jobs prioritise different characteristics, which is why all three types are still used.

Magnetic storage

Magnetic storage suits situations where large capacity at low cost matters more than speed or ruggedness, such as desktop bulk storage, servers and backup archives.

Optical storage

Solid-state storage

Comparing the three types

A good comparison weighs the same characteristics across all three. On capacity, magnetic hard disks lead (cheap terabytes), solid-state is catching up but costs more per gigabyte, and optical discs are smallest. On speed, solid-state is fastest (no moving parts), magnetic is moderate, and optical is slow. On durability and portability, solid-state is the most robust and is used in portable devices, magnetic disks are fragile while spinning, and optical discs are portable but easily scratched. On cost per gigabyte, magnetic is cheapest, then solid-state, with optical in between for small amounts. Matching these characteristics to a scenario is what exam questions reward.

Typical uses

Each type is chosen for the job that suits its characteristics. Magnetic hard disks suit bulk storage, servers and backups where large, cheap capacity matters more than speed. Solid-state suits laptops, phones, tablets and games consoles where speed, low power and ruggedness are worth the higher price. Optical discs suit distributing films, music and software, and read-only archiving, where a cheap, portable, write-once medium is enough. Understanding why each is suited to its use lets you justify a recommendation rather than just listing facts.

Try this

Q1. State why a computer needs secondary storage. [2 marks]

• Cue. To keep programs and data permanently because RAM is volatile and loses its contents when the power is off.

Q2. Give one advantage of solid-state storage over magnetic storage. [1 mark]

• Cue. It is faster and more durable because it has no moving parts.