Secondary storage

• What are the three common types of storage?

  • Optical
  • Magnetic
  • Solid state
• What do computers have secondary storage?

  Secondary storage is non-volatile, long-term storage. It is used to keep programs and data indefinitely. Without secondary storage all programs and data would be lost the moment the computer is switched off.
• Cost- what is the cost per gigabyte (GB)?
• Capacity - how much data can the medium hold?
• Speed of access - how quickly can data be transferred to and from the medium?
• Portability - how portable is the medium? Does it need to be portable?
• Durability - how robust is the medium, and how robust will it need to be?
• Reliability - how resilient and long-lasting is the medium?
• Secondary storage

  Data storage used to store data so that the computer can be switched off
• Optical

  Optical devices use a laser to scan the surface of a spinning disc made from metal and plastic. The disc surface is divided into lands (which are flat) and pits (which are like hollows).
• What are some examples of optical storage?

  • DVD
  • CD
  • Blu-ray
• What are the advantages of optical storage?

  • Very cheap (per GB)
  • Portable
  • Won't get damaged by water
• What are the disadvantages of optical storage?

  • Easily scratched
  • Slow read / write speed due to moving parts
• Magnetic

  Magnetic devices such as hard disk drives use magnetic fields to magnetise tiny individual sections of a metal spinning disk. Each tiny section represents one bit. A magnetised section represents a binary '1' and a demagnetised section represents a binary '0'. 
• What are some examples of magnetic storage?

  • Cassettes
  • Hard disk
• What are some advantages of magnetic storage?

  • Extremely low cost per GB
  • Very reliable
  • High in capacity
• What are some disadvantages of magnetic storage?


  • Vulnerable to magnetic fields
  • Slower read / write speed due to moving parts
  • Not very portable
• Solid State

  Solid state devices use non-volatile random access memory (RAM) to store data indefinitely .
• What are examples of solid state storage?

  • Solid-State Drive (SSD)
  • USB Flash Drive
• What are the advantages of solid state storage?

  • Very fast read / write access
  • Durable- no moving parts
  • Portable- small and no moving parts
• What are the disadvantages of solid state storage?

  • Cost- very high per a gigabyte
  • Reliability - Limited read / write cycles
• A section of secondary storage is partitioned to act as virtual memory.
• Data from RAM is transferred into virtual memory.
• Data from virtual memory is transferred back to RAM when needed.