secondary storage devices

• What is primary storage

  Key storage components of a computer system that allows it to function
• What is secondary storage

  Storage components that store data for a long period of time
• What are secondary storage devices

  Devices that are used as a form of permanent storage
• What is a hard disk drive

  A device made of metallic disks that stores data magnetically
• What are the main characteristics of HDD (2)

  • a number of circular metallic disks that are stacked ontop of each other
  • Read/write head hovers above each disk
• What is the suitability of of HDD

  • lots of moving parts which make it susceptible to damage, making it unsuitable for portable devices
• How does a HDD work (3)

  • Magnetic disks rotate at hgih speeds under an actuating arm
  • Read-write head on the actuating arm can access any part of the magnetic disk
  • changes in the direction of magnetism represent 1s and 0s
• What is an optical disk

  An electronic device that can be written to and read from using a low-powered laser beam
• What are the main characteristics of an optical disk (1)

  • A single spiral track that starts in the middle and goes towards the edge
• What is an optical disk suitable for

  Suitable for storing music, movies, games etc
• How does a read only optical disk work (4)

  • Data on the disk is encoded as a series of bumps.
  • Protective layer is put over the surface to prevent any corruption of data
  • Laser beam reads the bumps on the CD and interprets them as different elecetrical signals
  • Electrical signals are then converted into binary
• How does a writeable optical disk work (3)

  • Disk is coated with translucent photosensitive dye
  • To write to disk, a laser alters the state of a dye spot on the disk to make it opaque
  • A read laser interprets the amount of light reflected from each dye spot to create binary patterns
• What is a solid-state disk

  A device that uses intergrated circuit assemblies to store data
• What is the suitability of an SSD (2)

  • no moving parts, making it easily transportable
  • data will always remain quickly accessible
• How does an SSD work (3)

  • NAND flash memory cells organise data into pages which are then combined into blocks
  • to read/write to an SSD, blocks are allocated semiconductors at different areas of the drive, enabling fast access times
  • Semiconductors in SSD can retain their data as they use a floating gate transistor which is able to trap and store charge
• Compare the typical capacities of the three storage devices (3)

  • HDD: high capacity (1TB)
  • SSD: medium capacity (500GB)
  • Optical disk: low capacity (900MB)
• Compare the relative cost of the three storage devices (3)

  • HDD: medium
  • SSD: high
  • Optical disks: low
• Compare the portability of the three storage devices (3)

  • HDD: some
  • SSD: some
  • Optical disks: yes
• Compare the relative power consumption of the three storage devices (3)

  • HDD: high
  • SSD: low
  • Optical disks: high
• Compare the relative speed of access of the three storage devices (3)

  • HDD: medium
  • SSD: high
  • Optical disks: low
• Compare the latency of the three storage devices (3)

  • HDD: high
  • SSD: low
  • Optical disks: very high
• Compare the reliability of the three storage devices (3)

  • HDD: good
  • SSD: very good
  • Optical disks: fair
• Compare the physical sizes of the three storage devices (3)

  • HDD: large
  • SSD: small
  • Optical disks: large