Secondary Storage

This lesson covers secondary storage technologies: magnetic (HDD), optical (CD, DVD, Blu-ray), solid state (SSD, flash) and cloud storage. For the OCR H446 exam you must understand how each technology works at a physical level, and compare them in terms of capacity, speed, portability, durability and cost.

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Why Is Secondary Storage Needed?

Primary storage (RAM) is volatile — it loses its contents when the power is switched off. Secondary storage is non-volatile, meaning it retains data permanently (until deliberately erased). It is used for long-term storage of programs, files and the operating system.

Secondary storage is also much cheaper per gigabyte than RAM, although significantly slower.

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Magnetic Storage — Hard Disk Drives (HDDs)

How an HDD Works

An HDD stores data on one or more spinning platters coated with a ferromagnetic material. Data is read and written by a read/write head that floats just above the platter surface on a cushion of air.

        Spindle
          |
    +-----+-----+
    |     |     |    <-- Platters (spinning discs)
    |     |     |
    +-----+-----+
          |
    Read/write head ----- Actuator arm

Key Terminology