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Process Model, Creation, States and Control Block

A process model is a conceptual framework used to understand and manage the execution of processes within an operating system.

• It describes the different states a process can be in, the transitions between these states, and the various activities associated with each state.

Process creation is the mechanism by which new processes are generated within an operating system.

• This can occur through various methods, such as user requests, system initialization, or by another process.

  1. Request: A request is made to create a new process (e.g., a user command or system call).
  2. Process Control Block (PCB) Allocation: A new PCB is allocated for the new process.
  3. Memory Allocation: Memory space is allocated for the process’s code, data, and stack.
  4. Initialization: The process’s PCB is initialized, including setting up the program counter, registers, and priority.
  5. Linking to Parent: If the new process is created by another process, a parent-child relationship is established.
  6. State Transition: The new process is placed in the ready state, awaiting CPU allocation.

Example:

In UNIX-like systems, processes are created using the fork() system call, which duplicates the calling process. The new process (child) gets a copy of the parent’s address space and resources. The exec() system call can then be used to replace the child’s address space with a new program.

The Process Control Block is a data structure used by the operating system to store information about a process. It is essential for process management and context switching.

  • Process ID (PID): Unique identifier for the process.
  • Process State: Current state of the process (e.g., ready, running).
  • Program Counter: Address of the next instruction to execute.
  • CPU Registers: Values of the CPU registers for the process.
  • Memory Management Information: Includes base and limit registers, page tables, etc.
  • I/O Status Information: List of I/O devices allocated to the process, open files, etc.
  • Accounting Information: Includes CPU usage, process start time, and other statistical data.
  • Parent Process ID: Identifier of the parent process, if any.
  • Priority: Priority level of the process.
  • Pointer to Next PCB: Used to link PCBs in scheduling queues.

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