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Computer systems (Interrupts (Classes (Program (Generated by some…

- - - - Generated by some condition of instruction execution
        
        Arithmetic overflow
        
        Division by zero
        
        Attempt to execute illegal machine instruction
        
        Reference outside a user’s allowed memory space
    - - Timer within the processor
    - - By an I/O controller, signal completion of operation or error condition
    - - Failure
        
        Power failure
        
        Parity error
  - - - If an interrupt is pending, the processor suspends execution of the current program and executes the interrupt-handler
      - Part of the OS
  - - - Disable interrupts while an interrupt is being processed
      - The processor ignores any new interrupt request signal
      - When processor finishes interrupt, checks for more interrupts before resuming the program
    - - Allows an interrupt of higher priority to cause a lower-priority interrupt handler to be interrupted
      - If a I/O interrupt with higher priority is requested, the interrupt is honored. Otherwise, interrupt waits until current sequence is finished
- - - - The time it takes to read one word from or write one word to memory
  - - - Replacing algorithm
        
        Least-recently-used (LRU) algorithm
      - The more flexible the mapping function, the more complex is the circuitry required to search the cache to determine if a given block is in the cache.
    - - The writing can occur every time that the block is updated
      - The writing occurs only when the block is replaced
- - - - Exchange data with memory
        
        Registers :star:
        
        MAR (Memory Address Register)
        
        Specifies the address in memory for the next read or write
        
        MBR (Memory Buffer Register)
        
        Contains the data to be written into memory or which receives the data read from memory
        
        PC (Program Counter)
        
        Holds the address of the next instruction to be fetched
        
        Auto increments after each instruction fetch so that it will fetch the next instruction in sequence (unless instructed otherwise)
        
        IR (Instruction Register)
        
        Stores the fetched instruction
        
        Contains bits that specify the action to take
    - - Processor-memory
        
        Data may be transferred from processor to memory or from memory to processor
      - Processor I/O
        
        Data may be transferred to or from a peripheral device by transferring between the processor and an I/O module
      - Data processing
        
        The processor may perform some arithmetic or logic operation on data
      - Control
        
        An instruction may specify that the sequence of execution be altered (change PC)
  - - - Real memory
      - Primary memory
    - - Stores data and programs
      - Typically volatile: lost when shut down
    - - Set of locations, defined by sequentially numbered addresses
      - Each location contains a bit pattern that can be interpreted as either an instruction or data
  - - - Uses registers
        
        I/OAR (I/O address register)
        
        Specifies a particular I/O device
        
        I/OBR (I/O buffer register)
        
        Used for the exchange of data between an I/O module and the processor
- - - - Processor registers
      - Cache
      - Main memory
    - - Magnetic disk
      - CD-ROM
      - CD-RW
      - DVD-RW
    - - Magnetic tape
- - - - Whether a read or write is requested
      - The address of the I/O device involved
      - The starting location in memory to read data from or write data to
      - The number of words to be read or written
- - - - By using larger cache blocks
      - By incorporating prefetching mechanisms (fetching items of anticipated use)
  - - - By keeping recently used instruction and data values
      - Memory hierarchy
- - - - 1 The processor reads (fetches) instructions from memory one at a time
      - 2 Executes each instruction
    - - Halt
        
        The processor is turned off
        
        Some sort of unrecoverable error occurs
        
        A program instruction that halts the processor is encountered
- - - - Performance
        
        Greater
      - Availability
        
        Both can do same functions
      - Incremental growth
        
        Additional processors
      - Scaling
        
        Vendors offer a range of products
    - - Cache coherence