What is a Process Control Block?

Every process in the operating system is represented by a process control block as well called a task control block. It contains several pieces of information associated with a specific process such as

• Process state: The state perhaps new, ready, running, and waiting, halted and etc.
• Program counter: The counter point to the address of the next instruction to be executed for this process.
• CPU registers: The registers differ in number and type, depending on the computer architecture. They comprise index registers, accumulators, stack pointers and general purpose registers plus any condition code information. Along with PC, this state information has to be saved when an interrupt occurs, to permit the process to be continued correctly afterward.
• CPU scheduling information: This information comprises a pointer to scheduling queues, process priority and any other scheduling parameters.
• Memory management information: this information may comprise such information as the value of the base and limit registers the page tables or the segment tables depending on the memory system used by the OS.
• Accounting information: It comprise information about the amount of CPU and time limits, account numbers, real time used, job or process numbers and so on.
• I/O status information: The information comprises the list of I/O devices allocated to this process, a list of open files and so on.