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Introduction (Computing environments (Client-server (The client makes a…

- - - - these use wireless networks
      - to access web information
  - - - Ios
      - Android
  - - - Services/ is served
  - - - Single physical machine
- - - - Must be made
        piece by piece
  - - - A way to get the most of the computer
    - - Resource allocator
      - Control program
- - - - to process
      - users
  - - - From
        
        interal attacks
        
        external attacks
- - - - Shared memory
      - Competing for memory cycles
      - Different devices
        
        Bus connections
    - - Bootstrap
      - Stored in ROM
        
        EEPROM
        
        firmware
        
        Strarts the OS
        
        System daemons
        are created
    - - Interruptions are handled
        
        I/O
        
        System call
    - - These are grouped into 8
        
        Bytes
      - Programs are stored in bits
        
        These must be loaded
        
        main memory
        
        DRAM
        
        Volatile
        
        Small in comparison
        
        Secondary memory
        
        Persistent
        
        Slower
    - - Fetch
      - Decode
      - Execute
      - Store
      - PC++
  - - - Simpler
      - Limited
      - Usually include special puprpose procesors
      - General purpose
    - - Parallel
      - At least two processors
      - Increase throughput
      - Economy of scale
        
        Can be cheaper than multiple
        single processor computers
      - Increased reliability
        
        Graceful degradation
        
        Fault tolerant
      - Two types
        
        Symmetroc multiprocesing
        
        Assymatric multiprocessing
    - - Composed of individual systems
        
        Loosely coupled
      - High availability
      - Symmetric or assymetric
      - HPC environment
        
        Requires parallelization
        
        Distributed lock management
        
        Storage area nwteorks
  - - - CPU
      - I/O
      - Memory
    - - Is shaped based on user needs
- - - - Multiprogramming
        
        Several jobs in memory
        simultaneously
        
        Jobs are kept in the job pool
        
        these jobs are prioritized by the OS
        
        Job scheduling
        
        Involves memory allocation
        
        CPU scheduling
        
        When they are all ready, one is chosen
        
        If a job goes idle
        the OS switches execution
        to another
        
        Multitasking
        
        The CPU executes
        jobs by switching
        
        This changes are frequent,
        the user feels everything
        runs at the same time
      - A program loaded in memory
        
        process
        
        Memory management
        
        swapping between programs
        when there is not enough memory
        
        Virtual memory allows a
        program which is not in memory
        completley to run
  - - - waits for events
        to happen
        
        Inteuptions
        
        Traps
        
        These must be controlled
        properly by the OS
    - - Kernel mode
        
        privileged instructions
      - user mode
        
        in this mode
        
        the user
        
        asks the operating system
        to do tasks using syscalls
        
        Treated as a software
        interrupton
      - Allows us to tell who's
        code is running
      - There can be multiple levels
    - - prevents
        
        user programs for running too long
        
        intentionally
        
        by error
      - can either be
        
        fixed
        
        variable
  - - - Linux
        
        distributions
      - BSD Linux
      - Solaris
        
        SunOS
- - - - different to a program
        
        Programs are passive
        
        Processes are active
    - - resources
        
        CPU time
        
        memory
        
        files
    - - Scheduling executions
      - Creation and deletion
      - Suspension and resuming
      - mechanisms for synch
      - mechanisms for communication
  - - - Knowing what memory is used and by whom
      - Deciding what processes and data to move
      - allocating and deallocating as needed
  - - - logical ones
        
        files
    - - Os must
        
        Create and delete
        
        files
        
        directories
        
        Primitives for manipulation
        
        Secondary storage mapping
        
        back up on storage
    - - Space management
      - storage allocation
      - disk scheduling
    - - memory hierarchy
      - Principle of locality
      - cache coherency