Secondary Storage (Optical, Magnetic, Solid-State & Cloud)

• Secondary storage


  Any memory device not directly connected to the CPU, has to go through controllers and can't have a direct channel to the CPU
• Main memory (RAM)


  Has its own buses that connect directly to the CPU
• You need secondary storage to have long-term persistent (non-volatile) storage where data is kept when power is turned off
• You can't have a computer system without at least a connection to secondary storage to get instructions from and store data
• Secondary storage mediums


  • Speed (reading and writing)
  • Durability
  • Reliability
• Optical storage


  Stores data as binary 1s and 0s represented by variations of height (pits and lands) on the disk surface, read by reflecting light off the disk
• Evaluation of optical storage

  • Small capacity per unit
  • Fairly reliable and durable but can be easily damaged
  • Portable and easy to transport and store
• Magnetic storage


  Uses read/write heads with electromagnets to magnetize and demagnetize parts of the disk to represent data
• Evaluation of magnetic storage

  • Very large capacity
  • Comparatively cheap
  • Quite reliable but often stop working after a certain time
  • Not very durable, can be easily damaged
• Solid-state storage (SSD)


  Uses digital circuits and logic gates instead of a mechanical spinning disk, no need for defragmentation
• Evaluation of solid-state storage

  • Much faster read/write times than hard drives
  • More expensive per capacity
  • More reliable due to lack of mechanical parts
  • Silent and produce less heat
• Cloud storage


  Data stored on multiple remote servers, accessed over the internet
• Evaluation of cloud storage

  • Multiple versions of files kept for durability
  • Reliability of service may vary
  • Very portable, can access files anywhere with internet
  • Costs may be cheaper for large users due to economies of scale, but more expensive for smaller users