COMPUTER SCIENCE

• Binary


  Representing information using only 0s and 1s
• Computers only process binary digits (0 and 1), so characters such as letters, symbols and other numbers need to be converted into binary first
• Character set


  All the different characters a computer can represent
• Characters computers can represent

  • Alphanumeric characters (letters and numbers)
  • Commands (e.g. delete, space, enter)
• Converting binary into characters

  1. Key is pressed on keyboard

  2. Sends binary signal to computer

  3. Computer uses character set to translate binary code into corresponding character
• Character sets


  • ASCII
  • Extended ASCII
  • Unicode
• ASCII


  Can represent 128 characters, requires 7 bits
• Extended ASCII


  Can represent 256 characters, requires 8 bits
• Unicode


  Can represent 65,536 characters, requires 16 bits
• How character sets work

  1. Character is given a denary code

  2. Denary code is converted into binary

  3. Processed by computer and displayed on screen
• Pixel


  Picture element, a solid square of colour represented by a binary number
• Bitmap images


  • Made of pixels arranged on a grid
  • Each pixel assigned a binary value representing its colour
  • Quality depends on total amount of pixels (image resolution)
• Vector images


  • Drawn by computer following precise mathematical instructions to create lines and objects
  • Smaller file size than bitmap
  • Can be scaled up without loss in quality
• Metadata


  Information about the image that the computer requires to correctly display it
• Colour depth


  Number of bits per pixel
• Colour depth examples


  • 1 bit per pixel (2 possible colours)
  • 2 bits per pixel (4 possible colours)
  • 3 bits per pixel (8 possible colours)
  • 16 bits per pixel (over 65,000 possible colours)
• Resolution


  How tightly packed the pixels are
• More pixels


  Larger file size
• Sound


  A wave, vibrations that set particles in motion generating variations in pressure/density
• How sound is displayed on a computer

  1. Microphone measures change in air pressure

  2. Microphone translates air pressure into electrical voltage

  3. Analogue to digital converter digitises electrical voltage into bytes of information

  4. Computer displays the digitised sound for manipulation
• Sample rate


  Number of audio samples captured per second
• Bit depth


  Number of bits available to store an audio sample
• Bit rate


  Number of bits processed per second
• Higher sample rate, bit depth, bit rate


  Better audio quality
• Higher sample rate, bit depth, bit rate

  Larger file size
• Digital sound


  Digital representation of sound made up of thousands of snapshots/samples
• Analogue sound


  Graphical representation of sound, capturing change in air pressure and converting to electrical voltage
• Logic gates


  • AND
  • OR
  • XOR
  • NOT
  • NOR
  • NAND
  • XNOR
• AND gate


  • Requires both inputs on for the output to be on
• NOT gate


  • Output is always opposite to the input
• OR gate


  • Requires at least 1 of the 2 inputs to be on for the output to be on
• There are 3 fundamental logic gates: AND, NOT, OR
• Computer system


  Hardware and software that work together to process data and complete tasks
• Tasks performed by a computer

  • Accept data (input)
  • Store data (storage)
  • Process data (processing)
  • Output information
• Input device


  Hardware equipment used to provide data and control signals to be processed by the computer
• Examples of input devices

  • Keyboard
  • Mouse
  • Sensor
  • Microphone
  • Barcode scanner
• Storage


  Keeping data in memory
• Process


  Turning data into information by following software instructions
• Output device


  Hardware equipment that receives data from a computer, usually for display, projection or physical reproduction
• Examples of output devices

  • Screen
  • Printer
  • VR headset
  • Motor
  • Speaker