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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
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Memory Unit
- stores OS
- stores data currently in use
- stores software and the boot pragram
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Arithmetic Logic Unit (ALU)
- carries out arithmetic instructions
- carries out logical instructions
- acts as a gateway to the processor
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Register: Program Counter (PC)
- checks on where the next instruction is in the memory
- tell the processor where the next instruction is
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Register: Memory Address Register (MAR)
- where the address that was read from the PC is sent
- stores address here
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Register: Memory Data Register (MDR)
a copy of an instruction, that was in the address, is placed here
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Register: Current Instruction Register (CIR)
- the instruction is copied here
- instruction is split into its parts
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Register: Accumulator
carry out the task
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Data Bus
carries data being transmitted
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Address Bus
carries identification about where the data is being sent/ coming from
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Control Bus
carries control signals from the control unit to allow synchronisation of signals/commands to the processor
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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
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Random Access Memory (RAM)
- data is wiped clear when the power is switched off
- volatile
- e.g. applications software
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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
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Secondary storage: Optical
- CD's and DVD's: RW
- surface divided into sectors and has a single track
- indentations
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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
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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
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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
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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
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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
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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
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Peripheral device: printer
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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
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Peripheral device: speakers
- converts an alternating electrical current into sound
- Advantages: cheap, high quality sound
- Disadvantages: digital sound signal has to be converted
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Peripheral device: microphones
- digital sound saved for playback
- voice recognition
- Advantages: convert voice into text
- Disadvantages: take up alot of memory
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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
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Peripheral device: actuator
- used to control physical movement
- Advantages: easily controled, faults easy to diagnose
- Disadvantages: expensive, complicated
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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
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