4.1 Process concept

A process is a program in execution. A process is an active entity which includes the followings:

The program counter.

The processor's registers.

The stack.

A data section which contains global variables.

A heap.

Process state
A process changes its state while its activity is changing during the execution as shown in Figure 4.1. The process state can be one of the following:

New: The process is being created.

Running: Instructions are being executed.

Waiting: The process is waiting for some event to occur.

Ready: The process is waiting to be assigned to a processor.

Terminated: The process has finished execution.

4.1 Process concept

Figure 4.1: Diagram of process states (Silberschatz et.al., (2008)).

4.1 Process concept

Process control block
A process control block (PCB) is a data structure in the operating system kernel containing the information needed to manage a particular process. PCB includes the following information:

	Process state.
	Program counter.
	CPU registers.
	CPU-scheduling information.
	Memory-management information.
	Accounting information.
	I/O status information.