Operating System - Process Control Block

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In operating system, each process is represented by a Process control block. The PCB is also known as a task control block. The PCB is a data structure that contains all the information about a particular process.


Fig 1.Process Control Block

  • Process state:  current state of the process. It can be any one of the five states (new, ready, running, waiting and terminate).
  • Program counter  contains address of the next instructions is being to be executed for this process.
  • Process number:   Unique identification of the process.
  • CPU registers:   There are different CPU registers that are used by the process during execution.
  • CPU-scheduling:   contains information about process priority and scheduling.
  • Memory management:   contains the information of the base and limit register, page table and segment tables, depending on the memory system used by the operating-system.
  • Account Information:   contains information about the amount of CPU and real time used, time limits, account numbers, job or process numbers, and so on.
  • I/O Status Information:  contains information of I/O devices allocated to the process, a list of open files, and so on.

In short, PCB acts as the repository of information. This information may vary from process to process.


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