Computer science 4

• Input devices


  Input date/analogue/control signals through
• Processing System


  1. Processes it

  2. Displays the output
• Barcode reading


  1. Laser or LED light is reflected off the barcode

  2. Dark areas reflect no light

  3. Reflected light read by sensors

  4. Pattern generated is converted to digital data
• Barcode lookup


  1. Barcode number looked up in database

  2. Stock item record accessed

  3. Price and details sent to checkout

  4. Stock count reduced
• Stock level


  If below reorder level, new stock automatically ordered
• QR codes can contain more data than barcodes
• QR codes


  • Made up of blocks of light and dark squares (pixels)
  • Can hold up to 4296 characters or web addresses
• As more data is added, QR code structure becomes more complex
• QR code decoding


  1. Data converted to binary

  2. Decoded

  3. Displayed on screen
• QR codes


  Used for opening URLs and displaying data
• Advantages of QR codes

  • Can hold more info
  • Easier to read (no high tech readers needed)
• Disadvantages of QR codes

  • More than one QR code can be present
  • Susceptible to errors (but have built-in error checking)
• Barcodes contain almost no malicious code, unlike QR codes
• QR codes have data redundancy, making them more secure than barcodes
• Microphone operation


  1. Sound waves hit diaphragm

  2. Diaphragm vibrates

  3. Permanent magnet moves

  4. Electric current produced

  5. Converted to digital format
• Scanners


  Convert images into digital form that can be stored in computers
• 3D scanners


  • Take measurements along 3 coordinates
  • Produce 3D images that can be used in CAD
• Touch screens


  Use sensors to calculate touch location based on changes in electrical properties
• Actuator operation


  Converts electrical signal into mechanical motion to control devices
• LCD projector


  • Uses high intensity light beam passing through LCD display to project image
• DLP projector


  • Uses millions of micromirrors on a DMD chip to reflect light and form image
• Advantages of DLP projectors

  • High contrast ratio
  • Good for dusty/smoky environments
• Disadvantages of DLP projectors


  • Image can suffer from "rainbow" effect
  • No true grey scale
• Advantages of LCD projectors

  • Good color saturation
  • More energy efficient
• Disadvantages of LCD projectors

  • Lower contrast ratio
  • Shorter lifespan
• Inkjet printers


  • Use print head to spray ink droplets onto paper
  • Ink cartridges contain colored inks
• Inkjet printing technologies


  1. Thermal bubbles - heat vaporizes ink

  2. Piezo electric - crystal vibration forces ink out
• Cache- stores fequently used instructions, more cache means the processor can access more data, as RAM is slower
• ROM stores firmware, parts of the OS, and programs.
• RAM stores data that is currently in use and can be directly accessed by cpu, is volatile
• Virtual memory is used to run programs when there is insufficient RAM to run. It allows RAM to store more data
• OS and its functions

  
• How an interrupt works

  Processor finishes current FE cycle for program

  1. Processor checks interrupt priority queue

  2. Processor checks for higher priority interrupt than program

  3. Processor stores current process on stack

  4. Processor calls ISR for interrupt

  5. ISR resolves interrupt

  6. Processor retrieves content of stack to continue with process from program
• Digital currency


  A currency that does not exist physically, it can only be accessed electronically
• Blockchain


  • A decentralised database where each transaction is stored as a new set of data with a time-stamp and is linked to the previous set of data
  • Transactions cannot be altered, only new transactions added
  • Allows the location of the data to be traced
• Characteristics of a robot- it has mechanical parts/structure. It has electrical components. It is programmable.