Describe their relation and difference for process and program. Why the status of process is divided into five states, not other numbers, such as 4,7?    describe the contents of process control block.

Answer:

A program and a process is related term. The major difference between program and process is that program is a group of instructions to carry out a specified task whereas the process is a program in execution. While a process is an active entity, a program is considered to be a passive one.

Why the status of process is divided into five states, not other numbers, such as 4,7?   

When a process executes, it goes through a number of states. The current state of the process tells us about the current activity of the process. The state of a process may change due to events like I/O requests, interrupt routines, synchronization of processes, process scheduling algorithms, etc.

describe the contents of process control block.

All processes are represented in the operating system by a task control block or a process control block.

This contains many pieces of information connected with an exact process such as:

Process state, program counter, CPU registers, CPU scheduling information, memory management information, accounting information, I/O status information