What is process control block?

Each process is represented in the operating system by a process control block also called a task control block. It contains many pieces of information associated with a specific process. It simply acts as a repository for any information that may vary from process to process.
It contains the following information:
1 Process state
2 Program counter
3 CPU registers
4 CPU-scheduling information
5 Memory-management information
6 Accounting information
7 I/O status information