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Computer Science - Coggle Diagram

- - - - read and understand as the language used is closer to human language
      - write in a shorter time
      - debug at the development stage
      - maintain once in use
  - - - Programmers use assembly doe to...
        
        make use of special hardware
        
        make use of special machine-dependent instructions
        
        write code that doesn't take up much space in primary memory
        
        write code that performs a task quickly
    - - Is not usually used by programmers as it is difficult to understand and it can be complicated to manage data manipulation and storage
      - Takes up less storage
  - - - Translates a high-level language program into machine code
      - Produces an executable file in machine code
      - Produces error messages
      - Compiled programs can be used without the compiler
      - Compiled program is usually distributed for general use
    - - Executes a high-level language program a statement at a time
      - No executable file is produced
      - Interpreted programs cannot be used without and interpreter
      - Often used when a program is being developed
    - - Translates a low-level language program into machine code
      - An executable file of machine code is produced
      - Assembled programs can be used without an assembler
      - An assembled program is usually distributed for general use
- - - - Inkjet printer
        
        1) The data from the document is sent to a printer driver
        2) A check is made by the printer driver to make sure that the chosen printer is available
        3) Data is sent to the printer and stored in a temporary memory known as a printer buffer
        4) A sheet of paper is fed into the main body of the printer, a sensor checks if paper is available in the paper feeder tray
        5) As the sheet of paper is fed through the paper, the print head moves from side to side printing the text or image
        6) At the end of each full pass of the print head, the paper is advanced slightly to allow the next line to be printed
        
        Ink droplets are produced using...
        
        Thermal bubble
        
        Tiny resistors create localised heat which makes the ink vaporise. This causes the ink to form tiny bubbles. As the bible expands, some of the ink is ejected from the print head
        
        Piezoelectric:
        
        A crystal at the back of each ink reservoir is given a tiny electric charge which makes it vibrate and forces ink to be ejected
      - Laser printers
        
        1) Data from the document is sent to a printer driver
        2) A check is made by printer driver to ensure that the chosen printer is available to print
        3) Data is sent to the printer and is stored in the temporary memory known as a printer buffer
        4) A printing drum is given a positive charge as it rotates, a laser beam is scanned across it removing the positive charge in certain areas, this leaves negatively charged areas which match what needs to be printed
        5) The drum is coated with positively charged toner which only sticks to the negatively charged parts of the drum
        6) A negatively charged sheet of papers then rolled over the drum
        7) The toner on the drum sticks to the paper
        8) The paper goes through a fuser which melts the ink so that it fixes permanently to the paper
        
        Advantage over inkjet printers
        
        Carry out large print jobs faster and won't run out of ink halfway through
      - 3D printers
        
        A print head can move left and right, as well as up and down, and prints the object layer by layer using materials such as powdered resin, powdered metal, paper or ceramic powder
        
        1) A design is made using computer-aided design (CAD) software
        2) Finalised drawing is imported into some special software that prepares it in a format which is understood by the 3D printer
        3) The 3D printer is set up to allow the solid object to be made
        4) The solid object is built up layer by layer
        5) The object is removed from the 3D printer and is then prepared
    - - 1) Sound is produced from a computer by passing the digital data through a Digital to Analogue Converter
        2) This is then sent through an amplifier
        3) Finally sound emerges from a (loud) speaker
      - Sound is produced by voltage differences vibrating a cone in the speaker hosting at different frequencies and amplitudes
    - - LCD monitors
        
        The front layer of the monitor is made up of crystal diodes. These tiny diodes are grouped together in threes or fours which are known as pixels.
        
        LIQUID CRYSTAL DISPLAY/DIODE
        
        LED's
        
        LCD monitors are back lit using LIGHT EMITTING DIODE (LED) technology. Gives the image better contrast and brightness
        
        Advantages over CCFL technology
        
        CCFL uses 2 fluorescent tubes behind the LCD screen which supplies the light source
        
        LED's reach maximum brightness almost immediately
        
        Give a whiter light which sharpens the image and makes colours more vivid
        
        Produce a brighter light which improves colour definition
        
        Monitors using LED 's are much thinner
        
        LED's last almost indefinitely
        
        LED's consume very little power which means they produce less heat as well as using less power
        
        OLED's
        
        ORGANIC LIGHT EMITTING DIODES
        
        Use organic materials (made up of carbon compounds) to create semi-conductors which are very flexible
        
        Advantages of using OLED's compared to existing LED's and LCD's
        
        Plastic organic layers of an OLED are thinner, lighter and more flexible
        
        Give a brighter light than LED's
        
        OLED's do not require backlighting as they generate their own light
        
        Since OLED's require no backlighting, they use much less power than LCD screens
        
        Have a very large field of view, which makes them ideal for use in television set and for advertising screens
  - - - 2D Scanners
        
        Used to input hard-copy(paper) documents and convert them into electronic form
        
        1) Document is placed on a glass panel and then the cover is closed over it 2) A bright light illuminates the document 3) A scan head moves across the whole page and an image of the document is sent to the lens 4) The lens focuses the document image 5) Focused image falls on to a charged couple device and is turned into an electronic form 6) Software produces a digital image
        
        OPTICAL CHARACTER RECOGNITION (OCR) software allows the scanned text from a document to be converted into a TEXT FILE FORMAT. (used in airports)
      - 3D (laser) scanner
        
        Take several images along the x,y,z co-ordinates of an object to produce a 3D image here are numerous 3D scanners
        
        1) Object is placed on digitizer
        2) software drives a laser probe across the surface
        3) A laser moves across object while 2 cameras continuously rector the changing shape of the laser
        4) This is stored as millions f data points on computer and is merged into a 3D representation
    - - 1) Barcode is read by a red laser scanner or red LED (Light Emitting Diode)
        2) Light is reflected back off the barcode. Dark areas reflect little or no light
        3) Reflected light read by sensors (photoelectric cells)
        4) As laser is scanned across barcode, a pattern is generated and converted into digital data
      - Barcode has a lefthand side and righthand side separated bu guard bars. Different thicknesses of white and black lines represent numbers
    - - Read similar to barcodes except are read by an imagineer device such as a camera. Software on the app processes the image until it can be interpreted
      - Other differences
        
        QR codes can hold up to 7000 digits, barcodes can hold up to 30
        
        QR codes are read horizontally and vertically, where as barcodes are only read horizontally.
    - - 1) When you press a button to take a photograph, an aperture opens at the front of the camera and light streams in through the lens
        2) Light reflected off the object you are photographing hits a light sensitive cell behind the lens
        3) A sensor measures the colour and brightness of each pixel and stores it as a number
      - A microprocessor takes care of flash, focus, shutter speed, removing 'red eye' and other things
    - - 1) Each keyboard has an ASCII value. 2) Each character pressed is converted into a digital signal which the computer interprets
    - - 1) Red LED's detect movement in the x - y direction. 2) Software in the computer moves the cursor on your screen by a corresponding amount
      - Touchpad
        
        Contains a tactile sensor which allows user to move the cursor just by using their finger
    - - Are either built into computer or are external devices connected by USB
      - 1) When sound is picked up, a diaphragm vibrates 2) Vibrations produce an electric signal 3) Signal goes into a sound card and is converted into digital values and is stored in computer
      - Voice Recognition System
        
        1) User's voice is detected and then converted into digital, producing a digital wave pattern
        2) Software compares wave pattern to wave patterns stored in memory
        
        Only certain phrases can be used as system only recognises a few key phrases
      - Speech Recognition
        
        1) Spoken words are recognised and shown on a screen 2) These are then input into a word processor or used in another application 3) Compare spoken words to built-in dictionary
    - - Capacitive
        
        Made up of many layers of glass which act like a capacitor, creating electric fields between the glass plates in layers. When the top layer is touched, the electric current changes and the co-ordinates where it was touched is determined by an onboard microprocessor
        
        Advantages
        
        Medium cost technology
        
        Screen visibility is good even in strong sunlight
        
        Permits multi-touch capacity
        
        Screen is very durable
        
        Disadvantages
        
        Can only use bare fingers as a form of input
      - Infra-red
        
        Heat-sensitive
        
        Uses glass as the screen material. Need's warm object to carry out an input operation
        
        Optical
        
        Uses glass as the screen material. Uses an array of sensors (in the form of a grid). The point of contact is based on which grid co-ordinate is touched
        
        Advantages
        
        Both systems are multi-touch capabilities
        
        Optical system allows the use of bare fingers, gloved fingers or a stylus
        
        Both systems have good screen durability
        
        Disadvantages
        
        Relatively expensive technology
        
        Heat-sensitive system only allows bare finger to be used as input
      - Resistive
        
        Makes use of an upper layer of polyester and a bottom layer of glass. When the top polyester layer os touched, the top layer and the bottom layer complete a circuit. Signals are then sent out which are interpreted by a microprocessor, the calculations determine the co-ordinates of where the screen was touched
        
        Advantages
        
        Relatively inexpensive technology
        
        Possible to use bare fingers, gloved fingers or a stylus as input
        
        Disadvantages
        
        Screen visibility is poor in strong sunlight
        
        Doesn't permit multi-touch capacity
        
        Screen durability is only fair, vulnerable to scratches and the screen wears through time
    - - Sensors are devices which read or measure physical changes
      - Date read by sensors is a type of analogue date and needs to be converted to digital data for the computer to understand.
        
        DIGITAL TO ANALOGUE CONVERTER (DAC)
      - Types of sensors
        
        Temperature
        
        control a central heating system
        
        control/monitor a chemical process
        
        control/monitor the temperature in a greenhouse
        
        Moisture/humidity
        
        control/monitor moisture levels in soil in a greenhouse
        
        control/monitor humidity levels in the air in a greenhouse
        
        monitor dampness levels in an industrial application
        
        monitor moisture in a paint spray booth in a car
        
        Light
        
        switch street lighting on at night and off during the day
        
        monitor/control light levels in a greenhouse
        
        automatically switch on a car's headlights when it gets dark
        
        Infra-red/motion
        
        turn on the windscreen wipers on a car automatically
        
        detect intruders in a burglar alarm system
        
        count people entering/leaving a building
        
        Pressure
        
        detect intruders in a burglar alarm system
        
        weight things
        
        monitor/control a process where gas pressure is important
        
        Acoustic/sound
        
        pick up noise levels in a burglar alarm system
        
        detect the noise of liquids dripping in a pipe
        
        Gas (e.g O² or CO²)
        
        monitor pollution levels in a river or in the air
        
        measure O² and CO² levels in a greenhouse
        
        check for a CO² leak in a power station
        
        pH
        
        monitor/control acidity/alkalinity levels in the soil in a greenhouse
        
        pollution/environmental monitoring in rivers
        
        Magnetic Field
        
        any application where detection of changes in a magnetic field is required
        
        used in anti-lock braking systems in motor vehicles
      - Use in monitoring and control applications
        
        Sensor sends signal to microprocessor
        
        Signals converted to digital (if needed) using an ADC
        
        Microprocessor analyses data received by comparing it against stored values
        
        If new data is outside acceptable range, a warning message is sent to a screen to an alarm is activated
        
        The microprocessor has no effect on what is being monitored and is simply 'watching' the process
        
        If the new data is outside the acceptable range, the microprocessor sends signals to control valves, motor, etc.
        
        The output from the system affects the next set of inputs
- - - - All data bits from the original file are reconstructed when the file is uncompressed.
      - Lossless compression works by identifying repeating patterns in the file. These patterns can be replaced by pointers . This allows the file size to be reduced without losing any data.
    - - The file compression algorithm eliminates unnecessary bits of data
      - In MP3's they get rid of frequencies undetectable to humans or if 2 sounds are playing at the same time and 1 is almost undetectable, the converter gets rid of the quieter one
  - - - Random Access Memory (RAM)
        
        It is a volatile/temporary memory (the contents of the memory are lost when the power to RAM is turned off)
        
        It is used to store data, files, parts of the operating system that are currently in use
        
        It can be written to or read from and the contents of the memory can be changed
        
        The larger the size of the RAM, the faster the computer will operate
      - Read Only Memory (ROM)
        
        They are non-volatile/permanent memories (the contents of the memory remain even when the power to the ROM is turned off
        
        Often used to store start-up instructions when the computer is first switched one
        
        The data or contents of a ROM chip can only be read, they cannot be changed
    - - Hard Disk Drives (HDD)
        
        Data is stored on a digital format on the magnetic surfaces of the disks (or platters). A number of read-write heads can access all of the surfaces in the disk drive. Data is stored on the surface in sectors and tracks. A sector on a given track will contain a fixed number of bytes.
        
        HDD have very slow data access
      - Solid-state Drives (SSD)
        
        Have no moving parts and all data is retrieved at the same rate
        
        Most common type of solid-state storage devices store data by controlling the movement of electrons within NAND chips. The data is stored as 0s and 1s in millions of tiny transistors within the chip
        
        Benefits of using SSD instead of HDD
        
        more reliable (No moving parts to go wrong)
        
        considerably lighter (which makes them suitable for laptops)
        
        don't have to 'get up to speed' before they work properly
        
        have a lower power consumption
        
        run much cooler than HDDs
        
        are very things they have no moving parts
        
        data access is considerably faster
        
        Main drawback of SSD is the questionable longevity of the technology
    - - Optical storage systems
        
        CD/DVD disks
        
        Laserlight is used to read data and to write data in the surface of the disk
        
        Use a thin layer of metal alloy or light-sensitive organic dye to store the data
        
        Data is stored in 'pits' and 'bumps' on the spiral track. A red laser is used to read and write the data
        
        DVD's have larger storage as they use dual-layering
        
        DVD-RAM
        
        Instead of a single spiral track, they use a number of concentric tracks
        
        Use of concentric tracks allows simultaneous read and write operations to take place
        
        Allow numerous read and write operations and have great longevity which makes them ideal for archiving
        
        Blu-ray disks
        
        A blue laser rather than a red laser is used to carry out the red and write operations
        
        Using blue laser light means the pits and bumps can be much smaller as the wavelength is smaller and consequently, blu-ray can store up to 5 times more data than a normal DVD
        
        Blu-ray disks automatically come with a secure encryption system
      - Solid state storage systems
        
        USB flash memories
        
        Connect to a computer through a USB port
        
        Main advantage is they are small, lightweight devices
      - Magnetic storage systems
        
        Removable hard disk drives
        
        Essentially HDD but can be connected to the computer using USB ports