3.1.8 Secondary Storage

Table of Contents

Fork me on GitHub

1 Secondary Storage

Learn It

  • Unlike RAM, secondary storage is a more permanent way of storing data.
  • Secondary storage can be internal - such as a computer hard drive, or external - such as a memory stick.
  • Internal storage is used to store a computer's operating system, software and user files.
  • External storage is used for backing up data, transferring files, transporting files or as an extension to internal storage.

Learn It

  • There are three classes of secondary storage - Magnetic, Optical and Solid-State.
  • Secondary storage sizes are measured in bytes.
Bytes Name Abbreviation
1,000 Kilo 1kB
1,000,000 Mega 1MB
1,000,000,000 Giga 1GB
1,000,000,000,000 Tera 1TB
1,000,000,000,000,000 Peta 1PB
1,000,000,000,000,000,000 Exa 1EB
1,000,000,000,000,000,000,000 Zetta 1ZB
1,000,000,000,000,000,000,000,000 Yota 1YB

Learn It

Magnetic Storage

  • A disk that contains iron particles.
  • Particles can be arranged in one of two directions - representing 1 or 0
  • The drive contains a head that can read the direction of the particles and change the direction of the particles using an electromagnetic field.
  • The disk is spun rapidly, and the head moves back and forth, reading different parts of the disk.

Optical Storage

  • A disc that contains dents (pits) and flat spots (lands)
  • A laser shone on the disc will not be reflected it if hits a pit. This represents a 0.
  • The laser will reflect when it hits a land. This represents a 1.
  • The disc is spun rapidly and the laser guided over different parts of the disc.

Solid State Storage

  • These disks contain billions of transistors arranged to make memory cells.
  • The cells can be set to allow current to flow (1) or not to flow (0)
  • By detecting if current is flowing or not flowing through a particular cell, the 1 or 0 can be read.

Try It

  • Arrange the following advantages and disadvantages into the tables below.


  • Fairly quick
  • Easy to carry around
  • Extremely fast read and write speeds
  • Easy to use
  • Large capacity
  • Easily replaced or upgraded
  • Can be used in many types of devices (not just computers)
  • Long lasting (if cared for)
  • No mechanical requirements
  • Silent when used
  • Very cheap per MB of data
  • Light weight and small
  • Use very little power
  • Very cheap, and disposable
  • Very durable even if dropped or knocked around


  • Contains moving parts that will eventually fail
  • Limited storage capacity
  • Can be noisy
  • Easily broken if not protected
  • Use a large amount of power
  • Have read/write limits - a few 100000 times before cells become corrupt
  • Require special drives to read
  • Very expensive per MB of data
  • Can be easily damaged if dropped or knocked around
  • Fairly expensive per GB although price is rapidly dropping
  • Easily damaged by scratching, heat and light
  • Write speeds are slow, compared to read speeds.
Magnetic Advantages Magnetic Disadvantages Optical Advantages Optical Disadvantages Solid State Advantages Solid State Disadvantages

Learn It

  • Magnetic Storage is used in Hard Drives and tape drives. Tape drives are often used for backing up large volumes of data.
  • Optical Storage is used in CDs, DVDs and Blu-Ray.
  • Solid State is used in Hard Drives, Memory Sticks and Flash memory cards.

Try It

Answer the following questions:

  1. Explain how data can be read or written with a magnetic disk. (5 marks)
  2. Explain why digital video cameras are now more likely to use solid state storage rather than magnetic tape storage. (4 marks)
  3. Discuss three advantages and/or disadvantages of using cloud storage over a memory stick to transfer files between computers. (6 marks)