secondary storage

• Secondary storage


  Where all data, operating systems, applications and user files are stored when not in use
• Types of secondary storage

  • Magnetic hard disk drives
  • Solid state drives
  • CDs
  • DVDs
  • Blu-ray discs
  • USB pen drives
  • Memory cards
• Magnetic hard disk drives (HDDs)


  • Made up of a stack of magnetised metal disks spinning at 5400-15000 rpm
  • Data read magnetically in small areas called sectors within circular tracks
  • Read/write heads on a moving arm are used to access sectors on the disks
  • Generally very long lasting and reliable, although can be damaged by large impacts
• Solid state drives (SSDs)

  • Storage devices with no moving parts, most use flash memory
  • Significantly faster read/write times than HDDs
  • Can give much quicker times for booting up and opening programs and files
• Optical discs


  • CDs can hold around 700MB, DVDs around 4.7GB, Blu-Rays around 25GB
  • Come in three formats: read-only, recordable, and rewritable
  • Use laser to read/write data as microscopic indentations on the disc surface
• USB pen drives and memory cards

  • Also flash-based, solid-state storage
  • Much slower than SSDs and have a much shorter read/write life
  • Used to expand storage capacity of small devices like cameras, smartphones and tablets
• Advantages of HDDs


  • Cheaper
  • Higher capacity
  • Longer read/write life than SSDs
• Advantages of SSDs


  • Faster
  • More shock-proof than HDDs
  • Don't need defragmenting
  • Silent operation
• Magnetic tapes have much greater storage capacity than HDDs and an extremely low cost per GB
• Magnetic tapes


  • Used by large organisations to store huge amounts of data in archive libraries
  • Read/written sequentially, so slow when finding specific data but fast once in the correct place
• Optical discs are declining in use due to increased internet speeds and streaming/download services
• DVD-Rs and DVD-RWs used to be popular for backing up data, but can't compete with flash storage devices due to low capacity per disc, slow read/write speeds and poor reliability of RW discs
• Optical discs have some advantages - they're very cheap per GB, portable, and won't be damaged by water or shocks (although easily scratched)
• Storage media refers to the actual thing that holds the data, e.g. an optical disc. Storage devices read/write data to media, e.g. optical drives, or HDDs.