Ict

• Secondary storage


  All non-volatile storage devices that are not part of primary memory (RAM or ROM)
• Secondary storage devices


  • Storage capacity is much larger than RAM or ROM, but data access time is much longer
  • Store operating systems, application, photos, device drivers and other types of files/data
• Types of technology used by secondary storage devices


  • Magnetic
  • Optical
  • Solid state
• Storage device


  Hardware used to read data from or write data to a storage media
• Storage media


  Material on which the data is stored
• Magnetic storage media


  • Rely on the property that certain materials have magnetic properties (such as iron oxide) and these properties can be used to store data (1s or 0s)
  • Data is written by changing the local magnetic polarity to represent either a 0 or a 1
• Magnetic storage devices


  • Magnetic tape drive
  • Hard disk drive (HDD)

  
• Magnetic tape


  Stores data in a long line on magnetic tape and read by a magnetic tape drive
• Magnetic tape drive


  Device for collecting, backing up and archiving data on magnetic tape
• Uses of magnetic tapes


  • Batch processing (e.g. production of utility bills in large numbers overnight)
  • Backups of data for long-term storage/archiving
  • Daily backups in companies that handle large amounts of data
• Magnetic tapes


  • Have huge storage capacity, but data access time is very slow since the tape must fast forward or backward until the required data is found
• Hard disk drive (HDD)


  • Main storage device on most personal computers, but rapidly being replaced by solid state drive
  • Data is stored on disk surfaces (called platters) that are coated in a magnetic material
  • Data is stored in concentric circles on the surfaces known as tracks and sections within each track are called sectors

  
• Uses of HDDs


  • Store operating systems
  • Store system software
  • Store data (photos or music)
• Portable hard disk drives


  • Work in the same way as fixed HDD devices, but they are contained within their own cases and are separated from main computer systems
  • Main use is backing up data and to allow data to be transferred between computers
  • Use USB cables for transferring large amounts of data

  
• Portable hard disk drives


  • Small and light to be carried around
  • Can be used by multiple computers for file sharing
• Portable hard disk drives


  • Easily misplaced or stolen
  • Easily damaged as they are being moved (could be knocked or dropped)
• Optical storage media


  • Use light from lasers to read and write data onto plastic (polycarbonate) discs
  • Rely on the optical properties of certain chemical dyes and metal alloys to enable the storage of 1s and 0s

  
• Common types of optical storage devices


  • Compact discs (CDs)
  • Digital versatile discs (DVDs)
  • Blu-ray discs

  
• CDs and DVDs


  • Can be designated as 'R' (write once), 'RW' (read/write many times) and ROM (read-only)
  • Have a single spiral track running from the inside to the outside
  • Are split up into sectors and allow for direct access to data
  • Data is stored on the surface in pits (low points) and lands (high points) – these pits and lands are created when laser light writes data to the disk surface

  
• DVDs


  Have dual-layering (two polycarbonate disks are sandwiched together), which increases their storage capacity
• Blu-ray discs


  • Use blue laser light, which has a shorter wavelength than red laser light, increasing the storage capacity when compared to DVDs
  • Allow greater interactivity than DVDs, e.g. they allow the user to create playlists, reorder programmes stored, access websites and download subtitles/artwork
  • Have a much greater transfer rate than DVDs (at least four times faster), so they are well-suited to playback of High Definition (HD) or 4K/8K formats
  • Have a storage capacity of at least five times that of the equivalent DVD
• Solid state storage media


  • Use flash memory, which makes them much faster than traditional fixed hard disks
  • Flash memory consists of non-volatile memory chips containing transistors called floating gate transistors and control gate transistors that keep their charge even when the power is switched off
  • There are no moving parts
• Devices using solid-state storage media


  • Solid-state drives (SSDs)
  • Memory sticks
  • Flash memory cards
• Solid-state drives (SSDs)


  • A new generation of storage devices, rapidly taking over from HDDs as the main type of backing storage
  • Solid-state technology has enabled laptop computers to become thinner and much lighter, which has given rise to the development of smartphones and tablets
  • Portable SSDs, like portable hard disk drives, are contained within their own cases, and are often known as pen drives, thumb drives and memory sticks
• Pen drives (memory sticks)


  • Small solid-state storage devices that connect to a computer via a USB port
  • Used to back up files/data such as photos and music
  • Used to transport files/data between computers
  • Used as a security device (e.g. containing essential files to make software work) – called a 'dongle' when used in this way
  • When battery-powered, can be used as portable media (MP3) players
• Memory cards


  • Use solid-state technology
  • Similar to a memory stick, but it is flat and looks like a card which slots into a special port
  • Common types include SD card, XD card, and CFast card

  
• Flash memory is fast becoming the most common device for storage and for transferring data between devices
• Data/files are now often stored on remote cloud servers
• Music and movies are often streamed straight from the Internet, thus there is no need to store the music or movies on a computer
• Many televisions are now smart televisions and programmes can be streamed on demand, meaning DVD and Blu-ray players are no longer needed
• Comparison of different storage media and devices


  • Magnetic
  • Optical
  • Solid-state

  
• Comparison criteria


  • Capacity
  • Speed
  • Portability
  • Durability
  • Reliability
  • Cost