OPERATING SYSTEM BASICS

2.1. PROCESS LIFECYCLE

2.1.1 What is a Process?

A process is a program in execution. It is an active entity, unlike a program, which is a passive set of instructions stored on disk. A process requires resources such as CPU time, memory, files, and I/O devices to perform its task.

2.1.2 States of a Process

A process goes through several states during its execution. The major process states are:

1. New:
   The process is being created.

2. Ready:
   The process is waiting in the queue to be assigned to the CPU.

3. Running:
   The process is currently being executed by the CPU.

4. Waiting (Blocked):
   The process is waiting for some event (like input from a device) to occur.

5. Terminated:
   The process has finished execution and is being removed from memory.

2.1.3 Process Control Block (PCB)

Each process has a Process Control Block (PCB) which stores important information such as:

• Process ID

• Process state

• Program counter

• CPU registers

• Memory management information

• I/O status

• Accounting information

The OS uses the PCB to manage and track processes.