Process Management Basics

Introduction to Operating Systems

Process Management Basics is a core concept in Operating System that deals with how the operating system creates, schedules, executes, and terminates processes in a computer system.

Concept of Processes & Thread

1. Concept of Process

In Operating System, a process is a program that is currently executing.
It is an active entity that contains the program code and its current activity.

Components of a Process

A process typically consists of:

1.                      Program Code (Text Section) – Instructions to be executed

2.                      Program Counter (PC) – Address of the next instruction

3.                      CPU Registers – Temporary data used during execution

4.                      Stack – Stores function calls, local variables

5.                      Heap – Memory used for dynamic allocation

6.                      Data Section – Global and static variables

Example

When you open applications like:

• Google Chrome
• Microsoft Word

each running application becomes a separate process managed by the operating system.

Characteristics of a Process

• Each process has a unique Process ID (PID)
• Processes have separate memory spaces
• They can run independently
• Process switching requires context switching

2. Concept of Thread

A thread is the smallest unit of CPU execution inside a process.
It is sometimes called a lightweight process.

Multiple threads can exist within a single process and share the same resources.

Features of Threads

• Share same memory space
• Share files and resources
• Each thread has its own stack and program counter
• Faster creation and switching compared to processes

Example

In Google Chrome:

• One thread loads the webpage
• Another thread handles user input
• Another thread runs scripts

This allows tasks to run simultaneously within the same application.

3. Types of Threads

1. User-Level Threads

• Managed by user-level libraries
• Faster to create and manage
• OS does not directly manage them

2. Kernel-Level Threads

• Managed directly by the operating system kernel
• OS schedules them for execution

Example operating systems supporting kernel threads:

• Linux
• Windows

4. Difference between Process and Thread

Feature	Process	Thread
Definition	Program in execution	Smallest unit of execution
Memory	Separate memory space	Shared memory within process
Creation Time	Slower	Faster
Communication	Uses IPC	Easier (shared memory)
Resource Usage	Heavyweight	Lightweight

 ✅ Summary

• Process = Independent program running in memory.
• Thread = Smaller execution unit inside a process.
• Threads improve performance and
•  multitasking by allowing parallel execution.

Process State Diagram

In Operating System, the Process State Diagram shows the different states a process goes through during its lifecycle and how it moves from one state to another.

Basic Process States

1.                      New

o    The process is being created.

2.                      Ready

o    The process is ready to run and waiting for CPU allocation.

3.                      Running

o    The process is currently executing on the CPU.

4.                      Waiting / Blocked

o    The process is waiting for an event such as I/O completion.

5.                      Terminated (Exit)

o    The process has finished execution or has been stopped.

Process State Diagram (Text Representation)

Explanation of Transitions

New → Ready

• Process is admitted into the ready queue.

Ready → Running

• The CPU scheduler selects the process for execution.

Running → Waiting

• The process waits for I/O or another event.

Waiting → Ready

• The required event completes (e.g., I/O finished).

Running → Ready

• CPU time expires (preemption).

Running → Terminated

• Process execution finishes.

Key Idea

The operating system manages multiple processes by moving them between these states, ensuring efficient CPU utilization and multitasking.

✅ Short Exam Definition:
A process state diagram represents the lifecycle of a process and the transitions between states such as New, Ready, Running, Waiting, and Terminated.

Process Control Block (PCB)

In Operating System, a Process Control Block (PCB) is a data structure used by the operating system to store all information about a process.

Whenever a process is created, the operating system creates a PCB to keep track of that process during its execution.

Definition

Process Control Block (PCB) is a structure that contains all the information needed by the operating system to manage and control a process.

Each process in the system has its own PCB.

Information Stored in PCB

A typical PCB contains the following details:

1. Process ID (PID)

• A unique number assigned to each process.

2. Process State

• Indicates the current state of the process such as:
• New
• Ready
• Running
• Waiting
• Terminated

3. Program Counter

• Stores the address of the next instruction to be executed.

4. CPU Registers

• Contains the values of registers used during process execution.

5. CPU Scheduling Information

• Includes:
• Priority
• Scheduling queue pointers
• CPU scheduling parameters

6. Memory Management Information

• Includes:
• Base and limit registers
• Page tables
• Segment tables

7. I/O Status Information

• List of I/O devices allocated to the process.
• Open files.

8. Accounting Information

• CPU time used
• Time limits
• Process number

Simple Structure of PCB

Process ID (PID)         
Process State            
Program Counter          
CPU Registers           
CPU Scheduling Info      
Memory Management Info   
I/O Status Info         
Accounting Info      

Role of PCB in Context Switching

During context switching in Linux or Windows:

1.                      The current process state is saved in its PCB.

2.                      The next process state is loaded from its PCB.

3.                      CPU resumes execution of the new process.

Thus, PCB helps the operating system pause and resume processes efficiently.

✅ Short Exam Answer:

A Process Control Block (PCB) is a data structure used by the operating system to store information about a process such as process state, program counter, CPU registers, memory management information, and I/O status.

Inter-Process Communication (IPC).

In Operating System, Inter-Process Communication (IPC) refers to the mechanisms that allow processes to communicate and exchange data with each other.

Since processes usually run in separate memory spaces, IPC is needed for data sharing and coordination between them.

Why IPC is Needed

IPC is important for:

• Information sharing between processes
• Speeding up computation using multiple processes
• Resource sharing (files, printers, etc.)
• Process synchronization

For example, applications running on systems like Linux or Windows often communicate using IPC mechanisms.

Types of IPC

There are two main models of IPC:

1. Shared Memory

• Two or more processes share a common memory area.
• Processes read and write data in the shared space.

Features

• Faster communication
• Requires synchronization (semaphores, mutex)

Example
Process A writes data → Process B reads the same data.

2. Message Passing

Processes communicate by sending and receiving messages.

Two operations:

• Send(message)
• Receive(message)

Features

• Easier to implement
• No shared memory required

Common IPC Mechanisms

1.                      Pipes

o    Used for communication between related processes.

2.                      Message Queues

o    Messages are stored in a queue until read.

3.                      Shared Memory

o    Multiple processes access the same memory region.

4.                      Semaphores

o    Used to control access to shared resources.

5.                      Sockets

o    Used for communication between processes over a network.

IPC Model Diagram (Simple)

Process A  ----->  Message / Shared Data  ----->  Process B

Advantages of IPC

• Enables data exchange between processes
• Improves system efficiency
• Supports parallel processing
• Helps in process synchronization

✅Short Exam Definition:

Inter-Process Communication (IPC) is a mechanism provided by the operating system that allows processes to communicate and synchronize their actions by exchanging data.