Process Control Block (PCB)

 

Process Control Block:

PCB Stand for Process Control Block.  PCB is the Area in memory where the Operating system can find all the information it needs to know about a process, means PCB hold the information of all processes and keep track of all the processes. A process control block or PCB is a data structure (a table) that holds information about a process. Every process/ program / task that runs needs a PCB. When a user requests to run a particular program, the operating system constructs a process control block for that program.



The PCB contains important information about the specific process including: -

  • The current state of the process that is, whether it is ready, running, waiting, or whatever.
  • Unique identification of the process in order to track "which is which" information.
  • A pointer to parent process.
  • Similarly, a pointer to child process (if it exists).
  • The priority of process (a part of CPU scheduling information).
  • Pointers to locate memory of processes.
  • A register save area.
  • The processor it is running on.

1)      Process number of process ID: Each process is identified by its process number, process ID.

2)      Priority: They give the priority of different task.

3)      Process state: Each process may be in any of these states NEW, RUNNIGN, SUSPENDED and TERMINATED.

4)      Program counter: It indicates the address of the next instructions to be executed for this process.

5)      Registers: The include accumulator, general purpose, registers, index registers etc. Whenever a processor switches from one process to another process information about current status of the old process is saved in the register along with a program counter, so that the process to be allowed to continue currently afterwards.

6)      Accounting information: It include actual CPU time used in executing a process.

7)      Input and output status information: It includes I/O requests list of open files, information about collection of peripheral devices to process.

8)      Process scheduling details: It includes a priority of a process address to scheduling, queues and any other.

The PCB is a certain store that allows the operating systems to locate key information about a process. Thus, the PCB is the data structure that defines a process to the operating systems.

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