Process Control Block (PCB)
In the operating system, Process Control Block contains the information about the process which manages the scheduling of a particular process.
- Process state
- Program counter
- CPU registers
- CPU scheduling information
- Memory-management information
- Accounting information
- I/O status information
Process state: The state may be new, ready, running, waiting, halted, and SO on.
Program counter: The counter indicates the address of the next instruction to be executed for this process.
CPU registers: The registers vary in number and type, depending on the computer architecture. They include accumulators, index registers, stack pointers, and general-purpose registers, plus any condition-code information. Along with the program counter, this state information must be saved when an interrupt occurs, to allow the process to be continued correctly afterward.
CPU-scheduling information: This information includes a process priority, pointers to scheduling queues, and any other scheduling parameters.
Memory-management information: This information may include 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 operating system.
Accounting information: This information includes the amount of CPU and real time used, time limits, account numbers, job or process numbers, and so on.
Status information: The information includes the list of I/O devices allocated to this process, a list of open files, and so on.
The PCB simply serves as the repository for any information that may vary from process to process.