Storage devices and media

Backing storage device
1. non-volatile
  1. data is stored permanently
2. slower reading of data
Types of data access
1. Serial access
  1. data is accessed by starting at the beginning
    1. access each data in order
      1. till required information is found
  2. used on magnetic tape systems
2. Direct access
  1. used with magnetic disks and optical media (CDs and DVDs)
  2. key field used is able to calculate where data is stored
  3. access is much faster
back up data
1. able to retrieve data if the original storage device is hacked, lost or destroyed
Types of backing storage media
1. Solid State
  1. data stored as 1s and 0s
  2. consume much less power
  3. no moving parts
  4. Flash drives (memory sticks)
    1. transport files between computers or back up files
    2. compact and portable
    3. cheap to buy
    4. small: easy to lose
  5. Flash memory cards
    1. store photos on digital cameras
    2. store music files in MP3 players
    3. compact and robust
    4. expensive
    5. lower storage capacity than hard disks
2. Magnetic
  1. Hard disk drives
    1. Fixed hard disk
      1. Main backing storsage
      2. store operating system and working data
      3. very fast data transfer rate
      4. very large memory capacities
      5. can be easily damaged
      6. not portable
    2. portable hard disks
      1. connected to computer via USB
      2. transfer data, files and software between computers
      3. large memory capacity
      4. small and light
      5. can be easily damaged
  2. Magnetic tapees
    1. data is in serial acces
    2. robust
    3. useless in real time
    4. data transfer rate is fast
    5. access time is very slow
3. Optical
  1. can be read using light
  2. CD-ROM and DVD-ROM
    1. read only memory
    2. CD: store music files and software DVD: store films
    3. cheaper
    4. lower data transfer rate than hard disks
  3. portable
  4. store large data files
  5. CD-R and DVD-R
    1. recordable once only
    2. cheaper than RW disks
    3. once burned,it becomes ROM disks
    4. if error occurs, disk has to be thrown away
  6. CD-RW and DVD-RW
    1. re-writable media
    2. can be re-used several times
    3. used to record radio and TV programs
    4. might accidentally overwrite data
    5. expensive
  7. DVD-RAM
    1. able to watch a recorded program and record a new program at the same time
    2. have discrete concentric tracks
    3. use as satellite receivers to allow simultaneous recording and playback
    4. long life span (min. 30 years)
    5. writing is very reliable
    6. expensive
    7. less compatible
  8. Blue-ray disks
    1. large storage capacity
    2. fast data access and transfer rate
    3. expensive
    4. store and play back films

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Storage devices and media

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