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Processes (Concepts (Examples of interrupt :star: (Clock, I/O, Memory…

- - - - The allocation of main memory to processes
      - The allocation of secondary memory to processes
      - Any protection attributes of blocks of main or virtual memory, such as which processes may access certain shared memory regions
      - Any information needed to manage virtual memory
  - - - Whether the I/O device is available or assigned
      - The status of I/O operation
      - The location in main memory being used as the source or destination of the I/O transfer
  - - - Existence of files
      - Location on secondary memory
      - Current Status
  - - - Current state
      - Process ID
      - Location in memory
    - - Collection of program, data, stack, and attributes
      - To execute the process, the entire process image must be loaded into main memory or at least virtual memory
      - Elements
        
        User data
        
        User program
        
        Stack
        
        Process control block:star:
        
        Attributes
        
        Process identification
        
        Identifiers
        
        Processor state information
        
        User-visible registers
        
        Control and status registers
        
        PC
        
        Condition codes
        
        Status information
        
        Stack pointers
        
        Process control information
        
        Scheduling and state information
        
        Process state
        
        Priority
        
        Scheduling-related information
        
        Event
        
        Data structuring
        
        Interprocess communication
        
        Process privileges
        
        Memory management
        
        Resource ownership and utilization
        
        Most important data structure in the OS
        
        Contains all of the information about a process that is needed by the OS
- - - - Process management
      - Memory management
      - I/O management
      - Support functions
    - - Any time that the OS has gained control from the currently running process
      - Events
        
        Interrupt
        
        Trap
        
        Supervisor call
    - - 1 Save context of processor including program counter and other registers
      - 2 Update the process control block of the process that is currently in the Running state
      - 3 Move process control block to appropriate queue – ready; blocked; ready/suspend
      - 4 Select another process for execution
      - 5 Update the process control block of the process selected
      - 6 Update memory-management data structures
      - 7 Restore context of the selected process
- - - - New batch job
        
        The OS is provided with a batch job control stream, usually on tape or disk. When the OS is prepared to take on new work, it will read the next sequence of job control commands
      - Interactive log-on
        
        A user at a terminal logs on to the system.
      - Created by OS to provide a service
        
        The OS can create a process to perform a function on behalf of a user program, without the user having to wait (e.g., a process to control printing).
      - Spawned by existing process
        
        For purposes of modularity or to exploit parallelism, a user program can dictate the creation of a number of processes.
    - - Assign a unique process identifier to the new process.
      - Allocate space for the process.
      - Initialize the process control block.
      - Set the appropriate linkages.
      - Create or expand other data structures.
  - - - Normal completion
      - Time limit exceeded
      - Memory unavailable
      - Bounds violation
      - Protection error
      - Arithmetic error
      - Time overrun
      - Invalid instruction
      - Privileged instruction
      - Data misuse
      - I/O failure
      - Operator or OS intervention
      - Parent termination
      - Parent request
    - - A HALT instruction generating an interrupt alert to the OS.
      - A user action (e.g. log off, quitting an application)
      - A fault or error
      - Parent process terminating
- - - - Swapping:star:
        
        Involves moving part or all of a process from main memory to disk.
      - Other OS reason
      - Interactive user request
      - Timing
      - Parent process request
    - - The process is not immediately available for execution.
      - The process may or may not be waiting on an event.
      - The process was placed in a suspended state by an agent
      - The process may not be removed from this state until the agent explicitly orders the removal