ch 3 ict

• Storage Device


  Hardware component responsible for data storage

  
• Storage Media


  Physical material to store the data

  
• Backing up of data

  1. Copying of files to a different medium

  2. In case of a problem with the main secondary storage device
• Backing up of data

  Copying files to disk, tape, flash drive, or cloud storage
• Reasons to back up data

  • Data could be lost due to failure of the original storage device
  • Hackers could be responsible for the corruption or even loss of data
  • Data could be accidentally amended or overwritten on original medium
  • Data could be maliciously deleted from original medium
  • Backups are made in case the files need to be used elsewhere
• Serial access


  Necessary to start at the beginning of the file, then access each record in turn until the required record is found
• Direct access


  Uses the key field to calculate where data should be stored, able to access the data directly from the calculated position
• Serial access is a very slow form of data access
• Direct access is much faster than serial access
• When updating files with serial access, the old records/data are simply written over by the new records/data
• Direct access is used in real time operations such as controlling a chemical plant or online systems such as booking air tickets or automatic stock control
• Characteristics of backing storage

  • Non-volatile
  • Stores data permanently
  • Slower to access than internal memory
• Reasons why backing storage is needed

  • If computer is switched off, work in RAM is lost but backing storage stores data for future use
  • More likely that data is accidentally deleted in RAM
  • RAM is more expensive than backing storage per unit of memory
  • Software package may be so large that it is physically impossible for RAM to store it
  • Operating system may be so large that it is physically impossible for ROM to store it
  • Data may need to be transferred from one computer to another and can't do that with RAM
• Types of Backing Storage Devices

  • Magnetic (fixed hard disk, portable hard disk drives, magnetic tapes)
  • Optical storage media (CD/DVD disks, CD-ROM, DVD-ROM, CD-R, DVD-R, CD-RW, DVD-RW, DVD-RAM, Blu-ray discs)
  • Solid state storage media (solid state drives (SSD), memory sticks/pen drives, flash memory cards)

  
• Fixed (internal) hard disk drive (HDD)

  Used to store the operating system, applications software, used in real-time systems, online systems, file servers for computer networks

  
• Advantages of Fixed Hard Disks

  • Very fast data transfer rate and fast access times compared to CD/DVD
  • Very high storage capacity compared to CD/DVD
  • HDD is cheaper for larger amounts of storage space than Solid State drives
  • HDD has greater longevity for read/write functions than Solid State drives
• Disadvantages of Fixed Hard Disks

  • Read/write operation can be quite noisy compared to SSDs
  • Can be easily damaged if the correct shut down procedure is not carried out
  • Slightly slower to access than internal memory
  • They have many moving parts when compared to solid state drives (SSDs)
• Portable hard disk drives

  Used as backup systems to prevent loss of data, used to transfer files or software between computers

  
• Advantages of portable hard disk drives

  • They can be attached to and used by any computer that has a USB port
  • Holds large amount of data compared to CD/DVD
  • The data access time and data transfer rate are very fast
• Disadvantages of portable hard disk drives

  • The transfer rates are not as fast as with fixed drives
  • Their use with lots of different computers can mean there is a danger of viruses being transferred
  • It can be easily damaged if the user accidentally drops it or does not shut it down correctly after use
  • They are more expensive than other forms of removable media, such as CDs or DVDs
• Magnetic tapes


  Used for backups of file servers for computer networks, used to store large numbers of payroll records, used in long-term archiving of data, used in batch processing applications like clearing bank cheques, utility billing, producing pay slips
• Advantages of Magnetic Tapes

  • Less expensive than the equivalent capacity hard disk drive
  • Very robust
  • Have a huge data storage capacity
  • Tapes can be easily stored in a safe place
  • The data transfer rate is fast
  • Tapes are less prone to data loss and mechanical failure
• Disadvantages of Magnetic Tapes

  • Not suitable for an application that requires fast access to data
  • Updating files requires a new tape to be created
  • A special drive is required to read and write to them
• CD-ROM (Compact Disk Read Only Memory) and DVD-ROM (Digital Versatile Disk Read Only Memory)


  Optical disks that are read-only memory (ROM), cannot be written over, can only be read, used to store music files, software, computer games, large programs and films

  
• Advantages of CD ROM/DVD ROM


  • Cheaper to buy than hard disk drives
  • Once written, the data cannot be erased and this makes it useful for the distribution of software
• Disadvantages of CD ROM/DVD ROM


  • Data transfer rate is slower than for hard disks
  • Data access time is slower than for hard disks
• CD-R and DVD-R


  R means the disk is recordable once only, used for home recordings of music (CD-R) and films (DVD-R), used to transfer data from one computer to another, used in applications to prevent the deletion or overwriting of important data

  
• Advantages of CD R/DVD R


  • Cheaper than RW disks and hard disk drives
  • Physically impossible to accidentally delete important information stored on them

  
• Disadvantages of CD R/DVD R

  • If an error occurs during 'burning' the disc is damaged and must be thrown away (wasted)
• CD-RW and DVD-RW


  RW means these disks are rewritable, can be written over several times, used to record television programmes, used in CCTV (Closed Circuit Television) systems
• Advantages of CD-RW/DVD-RW


  • The data stored can be altered
  • Not as wasteful as the -R format. Even if burning fails, the disk can still be recorded on later and not thrown away

  
• Disadvantages of CD-RW/DVD-RW


  • More expensive to buy than CD/DVD-R disks
  • It is possible to accidentally overwrite data
  • The data transfer rate is lower than for a magnetic hard disk
  • Discs may stop working due to the repetitive erasing and writing
• Characteristics and uses of different types of DVD

  • DVDs are used to hold very large files several GB
  • DVDs used to store movies
  • DVDs discs can be used to store computer data
  • DVD RW used for applications which require the updating of information
  • DVD ROM used for applications which require the prevention of deletion of data
  • DVD ROMs used by software companies for distributing software programs and data
  • DVD ROMs used by movie distributors
  • DVD R used in applications which require a single 'burning' of data
  • DVD ROMs cannot have data changed
  • DVDs are portable and can be transported from one computer to another
• Blu-ray


  Blue laser, rather than a red laser, is used to carry out read and write operations, can store up to five times more data than a normal DVD
• Data transfer rate


  Lower than for a magnetic hard disk
• Optical discs


  • May stop working due to the repetitive erasing and writing
• DVDs are used to hold very large files several GB
• DVDs are used to store movies
• DVDs discs can be used to store computer data

  
• DVD RW


  Used for applications which require the updating of information