Chapter 3

• Storage Devices


  Hardware components that store digital data, programs, and information for later access and retrieval.
• Inside a computer we have primary storage and secondary storage
• Primary storage


  RAM and ROM
• RAM


  Volatile memory, whatever it stores disappears when computer is turned off
• ROM


  Stores boot instructions of the computer permanently, cannot be written to
• Primary storage


  • Small memory size compared to secondary storage
• Secondary storage/Backing storage


  Where data, application files, software are stored
• Secondary storage devices/media


  • DVDs
  • CDs
  • Hard disk drives
  • Solid state drives
• Storage media


  Hardware on which data is stored permanently
• Storage device


  Hardware used to read data from or write onto storage medium
• Types of storage media

  • Magnetic
  • Optical
  • Solid state
• Magnetic media


  • Use magnetism and magnetic field setup between disks and read/write head
• Optical media


  • Use laser light to read/write data
• Solid state media


  • Use logic gates and solid state technology to read/write
• Storage size units


  • Byte
  • Kilobyte
  • Megabyte
  • Gigabyte
  • Terabyte
• Sequential access


  Data read in the same order as stored
• Direct/Random access


  Data can be read instantly from any location
• Magnetic tape drives


  • Large storage capacity, used by large organizations for long-term data storage, slow access times
• Hard disk drives


  • Fast transfer rates and access times, large storage capacities, fragile with many moving parts
• Portable hard disk drives

  • Handy for software/data transfer, fragile, can be noisy
• Optical media use laser light to read/write data
• CD-R


  CD Recordable, can only be written to once
• CD-RW


  CD Rewritable, can be written, read, erased and rewritten multiple times
• CD-ROM/DVD-ROM


  Read-only, data cannot be modified
• Blu-ray discs


  • Higher storage capacity than CDs/DVDs due to layering technology
• CD-ROM


  Compact Disk Read Only Memory
• DVD-ROM


  Digital Video Disk Read Only Memory
• CD-ROMs and DVD-ROMs cannot be written to, only read from
• Optical media (CD-ROMs, DVD-ROMs)


  • Provide permanent storage
  • Prevent deletion or copy duplication of files
• Optical media (CD-ROMs, DVD-ROMs)


  Have slower data transfer rates and access times compared to hard disk drives
• Blu-ray discs


  • Use blue laser light instead of red laser light (used for CDs and DVDs)
  • Store up to 5 times more data than DVDs
• Blu-ray discs


  • Smaller pits and tracks for data storage
  • Can use dual layer technology to increase storage capacity
  • Use shorter wavelength blue laser light to penetrate deeper
  • Have secure encryption to prevent piracy and copyright infringement
• Advantages of Blu-ray discs


  • Large storage capacity
  • Fast data transfer rate and access speed
  • Content encryption to prevent piracy
• Disadvantages of Blu-ray discs

  • Relatively expensive
  • Encryption challenges when used to store videos
• Solid state drives (SSDs)

  Store data in millions of tiny transistors by controlling the flow of electrons, rather than using magnetic disks
• Solid state drives (SSDs)

  • More reliable than hard disk drives (HDDs)
  • No moving parts, so consume less power
  • Very fast access times (0.1ms vs 10ms for HDDs)
• Disadvantage of SSDs


  Limited number of rewrite operations (endurance limit), typically 3 years depending on usage
• Pen drives


  Small, lightweight, portable solid state storage devices
• Advantages of pen drives

  • Small, lightweight, and portable
  • Robust, not affected by magnetic fields
• Disadvantages of pen drives

  • Easy to misplace due to small size
  • Can get damaged if not ejected properly