Understand the role of secondary storage and the ways in which data is stored on devices (magnetic, optical, solid state).

What this dot point is asking

Edexcel wants you to explain why computers need secondary storage and to describe the three ways data is stored: magnetic, optical and solid-state devices, including their characteristics and which is suitable for a given use.

The role of secondary storage

The reason a computer needs secondary storage is straightforward: RAM is fast but volatile and limited, so it cannot keep your files between sessions. Secondary storage provides large, persistent, low-cost capacity, so your documents, photos and installed software survive a power-off. The trade-off is that it is slower to access than RAM, which is why programs are copied into RAM to run.

Magnetic storage

Magnetic hard disks offer very large capacity at a low cost per gibibyte, which makes them ideal for desktop computers, servers and bulk backup. Their weaknesses come from the moving parts: they are slower than solid state, noisier, use more power, and the spinning platters and moving head can be damaged by knocks, so they are less suited to portable devices. Magnetic tape is another magnetic medium, used for very large, cheap archival backups.

Optical storage

Optical discs are cheap to mass-produce and distribute, which is why films, games and software have been sold on them, and they are a convenient read-only or write-once medium. Their drawbacks are relatively small capacity compared with hard disks, slower access, and vulnerability to scratches. As downloads and streaming have grown, optical media are used less, but Edexcel still expects you to know how they work and when they suit a task (low-cost physical distribution).

Solid-state storage

Because there are no moving parts, solid-state storage is fast, durable (shock-resistant), silent, compact and low-power, which is why it is used in smartphones, tablets and modern laptops, and increasingly in desktops. Its main drawback is a higher cost per gibibyte than magnetic storage, and memory cells wear out after very many writes (though this is rarely an issue in normal use). For portable and performance-critical devices, the speed and durability usually outweigh the cost.

Comparing the three

The choice between the three is always a balance of cost, capacity, speed, durability and power. Magnetic wins on cost per gibibyte and raw capacity; solid state wins on speed, durability, size and power; optical wins on cheap physical distribution. A good exam answer states the property that matters for the scenario and links it to the device, rather than just naming a type.

Try this

Q1. State why secondary storage is described as non-volatile. [1 mark]

• Cue. It keeps its data even when the power is turned off.

Q2. State one advantage of solid-state storage over a magnetic hard disk drive. [1 mark]

• Cue. Any one of: faster access; no moving parts so more durable; lower power; smaller and lighter; silent.