This book provides a comprehensive overview of the fundamental concepts and principles behind modern operating systems. It covers key topics such as process management, memory management, file systems, and I/O systems. With a focus on both theory and practical applications, the book delves into the architecture and design of operating systems, offering insights into scheduling algorithms, concurrency, and resource allocation. Real-world examples and case studies from popular operating systems like Windows, Linux, and macOS are included to illustrate concepts. Designed for beginners, this book simplifies complex topics, making it an essential resource for students and aspiring IT professionals aiming to understand the backbone of modern computing.