Operating Systems and Computer Architecture 

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  • Operating Systems and Computer Architecture
    • Operating Systems
      • essentially the software running in the background of a computer system
        • without this many computers wouldn't be user friendly
      • it manages the basic functions of a computer
        • e.g. human computer interface, multitasking, batch processing, security, error handling
        • e.g. windows
      • Only loaded onto memory is ROM's initiating programs find no errors, in checking procedure
      • simple devices with embedded microprocessors - may not have os
    • Interrupts and Buffers
      • interrupt = signal sent from device to processor that causes the processor to stop and attend to interrupt
        • can occur when: disk drive is ready to receive more data, an error has occurred, a user has pressed a key that interrupts the process, a software error has occurred
        • when this is received the processor will either stop task entirely or continue task
          • whenever an interrupt is serviced the previous task's progress is saved using an INTERRUPT HANDLER
        • allows for many windows to be open simultaneously
      • Buffers = used in computers as temporary memory area. Essential because hardware devices operate slower than the processor.
        • buffers ensure that the processors don't spend their time waiting for the hardware
      • often used together
    • Computer Architecture
      • Von Neumann
        • idea of a stored program computer. Means many programs/data are held in memory and then moves between memory unit and processor
          • control unit
            • controls operations of the memory, processor and input/output devices
            • reads instruction, interprets instruction, sends signals using control bus
          • input and output devices
            • main method of entering and receiving data in computer systems
            • input = convert external data into a form that the computer can understand and process
            • output devices = show the results of computer processing in a way humans can understand
      • buses
        • data bus
          • bi-directional sends data between mu and p and input and output
        • control bus
          • unidirectional and bi-directional, carries signals relating to control and coordination of activities
        • address bus
          • unidirectional, carries signals relating to address between the mu and the p
            • address = were data is stored
      • registers
        • needed to manipulate data within the computer
        • high speed storage area within a computer, all data must be represented in a register prior to processing
      • memory unit
        • made up of a number of partitions
          • each partition has an address and its contents
            • contents = binary stored in the location
        • MAR = memory address register MDR= memory data register ALU= arithmetic and logic unit PC = program counter CIR= current instruction register
          • MAR and MDR
            • the memory location is sent to the MAR first
              • then read signal = sent to computer memory using a control bus
                • then contents is sent to MDR
                  • for a write function = order same but MAR assigns a memory location
          • ALU stored in processor
    • Fetch-Execute Cycle
      • to carry out a set of instructions
      • processor = fetches some data from memory and stores them in suitable registers
        • both address and memory bus are used
        • MAR -> PC-> CIR
          • pc = incremented before next instruction can be processed
      • execute = happens after the instructions are decoded
        • processor passes the decoded instructions as a set of control signals to the appropriate computer system components
          • 1. PC - contains address of the memory location of the next instruction to be fetched
            • 2. address copied to MAR using address bus
              • 3. instructions at MAR temp. copied to MDR
                • 4.contents of MDR copied to CIR
                  • 5.PC value incremented - points to next instruction
                    • 6. instruction finally decoded + executed
      • pc = address of the next instruction CIR = current instruction being processed

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