What is a PCB (process control block)? What is its significance in the kernel?

A process control block or PCB is a data structure (a table) that holds information about a process. Every process or program 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 i.e., 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.