computing

• NOT gate (Ā)

  0 -> 1

  1 -> 0

  
• AND gate (A.B)

  0+0 -> 0

  0+1 -> 0

  1+0 -> 0

  1+1 -> 1

  
• OR gate (A.B)

  0+0 -> 0

  0+1 -> 1

  1+0 -> 1

  1+1 -> 1

  
• XOR gate (A⊕B)

  0+0 -> 0

  0+1 -> 1

  1+0 -> 1

  1+1 -> 0

  
• conversions 1

  .

  
• conversions 2

  bits to bytes

  
• for every binary shift to the right, the number is halved

  e.g. binary shift by 3 = divided by 8
• for every binary shift to the left, the number is doubled

  e.g. left binary shift by 2 = multiplied by 4
• why do programmers prefer hexadecimal?

  • easier to convert
  • easier to write
  • shorter > less chance of error
• limitations of ASCII:

  • only uses 7 bits so can only represent 128 characters
  • cant represent characters from other languages
• unicode

  • covers all major languages
  • tries to cover every possible letter or symbol
• total number of colours:

  $2^n$

  e.g. 4 bit image has 16 colours
• file size (bits) colour

  • image size x colour depth
  • width x height x colour depth
• what does a high image size/colour depth mean?

  • higher quality image
  • increases file size
• file size (bits) sound

  sample rate(Hz) x sample resolution x time(s)
• what does increasing the sample RATE do?

  • better quality
  • closely matches original recording
  • increase file size
• what does increasing sample RESOLUTION do?

  • picks up quieter sounds
  • closer to quality of original
  • increase file size
• lossy compression

  permanently removes data

  e.g - MP3, AAC > audio

  - JPEG > image
• lossless compression

  temporarily removes data

  e.g - FLAC > audio

  - PNG, TIFF > image
• lossy (pros)

  • greatly reduces file size > more files can be stored
  • less bandwidth > downloaded and streamed quickly
  • lots of software can read lossy files > commonly used
• lossy (cons)

  • loses data
  • cant be used on text / software files > need to retain all orginal information
  • worse quality
• lossless (pros)

  • no reduction in quality
  • can be used in text / software files
  • can be decompressed
• lossless (cons)

  • only slight reduction in file size
• hardware

  • physical components of a computer
  • e.g. CPU, motherboard
• software

  • programs that run on a computer
  • e.g. word processor, web browser
• embedded system

  • computers built into other devices
  • e.g. microwave, dishwasher