data representation (1)

• computer uses binary as it only understands 0s and 1s, on and off switches.
• nibble


  4 bits
• byte 


  8 bits
• kibibyte


  1024 bytes
• mebibyte (MiB)


  1024 KiB
• gibibyte (GiB)


  1024 MiB
• tebibyte (TiB)


  1024 GiB
• pebibyte (PiB)


  1024 TiB
• exbibyte (EiB)


  1024 PiB
• hexadecimal


  use for humans to read and remember than binary.

  used in colour values, MAC address, IPv6 addresses, unicode
• analog sounds


  they are continuous
• digital sounds


  they are discrete - doesn't flow
• sounds are digitalised by sampling the sound wave a thousands of times per second and then converting the samples in binary
• recording quality improves

  • the more frequently we sample the sound (sample rate)
  • the more accurately we record the wave height (bit depth or sample resolution)

  both of these result in a larger sized file
• sample resolution


  the number of bits that are used per sample that provides the variation in amplitude that can be stored for each sample that determines how quiet or loud the sounds are that can be recorded
• to record sound the amplitude / height of the soundwave emitted must be measured and recorded (sampled) at regular intervals
• ASCII

  American Standard Code for Information Interchange

  consists of 128 characters, using 7 bits
• Unicode 


  uses 16 bits per character. helps represent most of the characters in international languages
• pixel


  smallest identifiable area of an image
• image resolution


  number of pixels in the image

  (area of pixels = image resolution)
• file size = colour depth x resolution
• sound rate


  this affects the levels of detail in digital representation
• lossy compression


  leaves out some data to compress, leaves out ranges that humans can't hear easily. decreases the quality
• lossless compression


  leaves all frequencies in file.

  it finds repeating groups of data and records data only once along with the number of times it was repeated
• lossy compression formats


  • JPG
  • MP3
  • WMV
  • MPG
• lossless compression


  • TIF
  • PDF
  • GIF
  • PNG
  • ZIP
• disadvantages of lossy compression


  the detail is permanently lost by reducing the colour depth, resolution or sample rate
• disadvantages of lossless compression


  less significant reduction in file size
• advantages of lossy compression

  smallest file sizes, least transmission time, reduces internet traffic and collisions
• advantages of lossless compression


  original quality is preserved / no information or data is lost