1.2 Memory and Storage

• RAM


  • Volatile
  • Holds open programs and data
• ROM


  • Non-volatile
  • Contains the program that runs when the computer boots
  • Loads the OS from storage onto RAM
• Secondary storage


  Large non-volatile, long term storage for programs and data
• Secondary storage


  • May be used as virtual memory when RAM is full
  • Magnetic - reliable, large capacity, not durable
  • Optical - portable, reliable, not durable
  • Solid state - fast read/write speeds, durable, expensive
• Data units

  • Bit
  • Nibble
  • Byte
  • Kilobyte
  • Megabyte
  • Gigabyte
  • Terabyte
  • Petabyte
• Binary addition: 1+1=1 carry 1, 1+1+1=1 carry 1
• Characters


  • ASCII - 8 bits per character, 256 characters
  • Unicode - can represent thousands of characters
• Images

  • Resolution - number of pixels
  • Colour depth - number of bits per pixel
• Metadata


  Data about data: height, width, colour depth, file type, camera modes, date
• Sound

  • Analogue sound converted to digital by taking samples of the amplitude at regular intervals
  • Sample rate (Hz) - number of samples per second
  • Bit depth - number of bits per sample
• Compression


  • Lossy - deletes part of the file, reduces file size but loses quality
  • Lossless - represents the file more efficiently without deleting any data
• Lossy compression is effective but means a loss of quality, not a big deal with images and sound. Lossless compression can't be used on text files and program files as all data is important.
• The Cloud - Benefits


  May be free of cost

  easier to share files

  less hardware

  easy to upgrade storage

  can be access anywhere

  backups are centeralised or automatic
• The Cloud - Drawbacks

  Connection can be slow

  May have to pay

  Login details may be forgotten

  Easy to hack into

  Can only be accessed if theres a connection

  Data leaks are common - trust in company