systems software

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  • Created by: helenalr
  • Created on: 02-06-22 16:56
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  • systems software
    • functions of an operating system
      • user interface
        • hides complexity of hardware from user
      • memory management
        • allocates RAM to programs and data
        • paging
        • segmentation
        • virtual memory
      • interrupt handling
        • CPU can be interrupted when necessary
        • stack
        • interrupt priority
      • processor scheduling
        • round robin
        • first come first served
        • shortest remaining time
        • shortest job first
        • multi level feedback queues
    • types of operating system
      • distributed
        • program can be run that uses data/resources from another computer
        • form of parallel processing
      • multi-tasking system
        • multi-user, multi-tasking
      • mobile
        • specific hardware (Android or iOS)
        • Android is open source
      • embedded
        • very limited for specific hardware
        • microwave!!
      • real time
        • responds to inputs quickly
        • medical equipment, auto pilot
    • utility programs
      • disk defragmenter
        • reorganises files to be in sequential blocks
      • automatic backup
      • automatic updating
        • runs in background to detect and install software updates
      • virus checker
        • scans and compares files to known viruses
      • compression software
        • reduces file size so they can be sent more easily
          • lossy vs lossless
    • application software
      • off the shelf
        • ready-made for anyone to buy
      • bespoke
        • custom made
      • open source
        • anyone can access, use, edit and sell
      • freeware
        • free but not open source
      • closed source
        • proprietary, must pay and follow restrictions
    • translators
      • assembler
        • low level into machine code
        • hardware specific
      • interpreter
        • line by line
      • compiler
        • bytecode  = combination / midpoint
          • interpreter
            • line by line
        • faster
        • hardware specific
        • translates whole program
    • stages of compilation
      • 1) lexical analysis
        • tokenising
      • 2) symbol table
        • lexer
      • 3) syntax analysis
        • phrases parsed
      • 4) semantic analysis
        • checks if program is valid
      • 5) code generation
        • optimisation
    • linker
      • put appropriate memory addresses in place so program can call/return library function
    • library
      • pre-written functions or user can write own
    • loader
      • copies program and any linked subroutines into main memory to run
  • compiler
    • bytecode  = combination / midpoint
      • faster
      • hardware specific
      • translates whole program

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