Secondary Storage

This lesson covers the three main types of secondary storage — magnetic, optical, and solid-state — their characteristics, advantages, disadvantages, and suitable uses. This is a key topic for AQA and OCR GCSE Computer Science.

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What Is Secondary Storage?

Secondary storage (also called external storage or permanent storage) is storage that is non-volatile — it retains data even when the computer is powered off. Unlike RAM, secondary storage is not directly accessed by the CPU during the fetch-decode-execute cycle. Instead, data must be loaded from secondary storage into RAM before the CPU can use it.

Why Is Secondary Storage Needed?

• RAM is volatile — all data in RAM is lost when the computer is turned off.
• Secondary storage provides a permanent place to save programs, files, and the operating system.
• Without secondary storage, you would lose everything every time you shut down.

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Types of Secondary Storage

1. Magnetic Storage

Magnetic storage devices store data using magnetised particles on a spinning surface. The read/write head magnetises tiny areas of the disk surface to represent binary 0s and 1s.