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2011-05-26 13:27:42
Computing Fundamentals

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  1. Control Unit (CU)
    • manages the execution of instructions
    • fetches instruction, decodes it then synchronises its execution
    • sends contol signals to other parts of the computer
    • uses a contol bus
  2. Memory Unit
    • stores OS
    • stores data currently in use
    • stores software and the boot pragram
  3. Arithmetic Logic Unit (ALU)
    • carries out arithmetic instructions
    • carries out logical instructions
    • acts as a gateway to the processor
  4. Register: Program Counter (PC)
    • checks on where the next instruction is in the memory
    • tell the processor where the next instruction is
  5. Register: Memory Address Register (MAR)
    • where the address that was read from the PC is sent
    • stores address here
  6. Register: Memory Data Register (MDR)
    a copy of an instruction, that was in the address, is placed here
  7. Register: Current Instruction Register (CIR)
    • the instruction is copied here
    • instruction is split into its parts
  8. Register: Accumulator
    carry out the task
  9. Data Bus
    carries data being transmitted
  10. Address Bus
    carries identification about where the data is being sent/ coming from
  11. Control Bus
    carries control signals from the control unit to allow synchronisation of signals/commands to the processor
  12. Read Only Memory (ROM)
    • data that is held on here cannot be altered
    • data is not erased when power is switched off
    • non-volatile
    • e.g. boot program
  13. Random Access Memory (RAM)
    • data is wiped clear when the power is switched off
    • volatile
    • e.g. applications software
  14. Secondary storage: Magnetic
    • Hardrive: consists of a series of disks (platter), increases volume of data, speed of access, divisions on surface of disks, format disk
    • Magnetic tape: archiving files, old device, data stored linearly, access time is slow
  15. Secondary storage: Optical
    • CD's and DVD's: RW
    • surface divided into sectors and has a single track
    • indentations
  16. Secondary storage: Solid-state
    • flash memory or USB stick
    • no moving parts
    • data is stored in a thin layer of oxide between non-conductive layers
  17. Peripheral device: barcode readers
    • uses a laser beam to read the code
    • Advantages: fast, reliable, check digit makes it good at rejecting errors
    • Disadvantages: input limited to numbers
    • Uses: identification of packages, tills in shops
  18. Peripheral device: MICR
    • magnetic ink character recognition
    • uses a special ink and reads number when passes through the MICR
    • Advantages: high level of security, automation
    • Disadvantages: expensive system, accept a few characters
    • Uses: cheques
  19. Peripheral device: OCR
    • converts a scanned image of text into an actual text file by recognising each character
    • Advantages: converts large amounts of text, can edit text
    • Disadvantages: poor recognition
  20. Peripheral device: OMR
    • uses IR light to scan marks on prepared forms
    • Advantages: quick and reliable
    • Disadvantages: has to be simple data capture forms, cannot be used for text and number input
    • Uses: multiple choice tests, lottery tickets
  21. Peripheral device: scanner
    • uses reflected light to read from a paper document
    • Advantages: scanned image can be enhanced
    • Disadvantages: loss in quality, lots of memory space
  22. Peripheral device: printer
    • dot matrix
    • inkjet
    • laser
  23. Peripheral device: plotter
    • prints by moving a pen sideways over the surface of a sheet of paper
    • Advantages: accurate, produce larger printouts
    • Disadvantages: slow, expensive, cannot print photographic images
  24. Peripheral device: speakers
    • converts an alternating electrical current into sound
    • Advantages: cheap, high quality sound
    • Disadvantages: digital sound signal has to be converted
  25. Peripheral device: microphones
    • digital sound saved for playback
    • voice recognition
    • Advantages: convert voice into text
    • Disadvantages: take up alot of memory
  26. Peripheral device: sensor
    • detects changes in physical or chemical environment and converts them into electrical signals
    • Advantages: huge range of possible sensors
    • Disadvantages: need an interface to convert analogue signals
  27. Peripheral device: actuator
    • used to control physical movement
    • Advantages: easily controled, faults easy to diagnose
    • Disadvantages: expensive, complicated
  28. Transfer of data
    • Buffers
    • Interrupts
    • Data is sent to the buffer from the primary memory
    • An interrupt is sent once the buffer is full
    • Buffer is emptied to storage device
    • Once the buffer is empty an interrupt is sent to the processor to request buffer refill