An Operating System (OS) is system software that manages computer hardware and software resources while providing common services for computer programs. It acts as an intermediary between users and the computer hardware, enabling the execution of applications efficiently and securely.

Key Functions of an Operating System:

1. Process Management – Handles running applications, multitasking, and resource allocation.
2. Memory Management – Manages RAM, allocates memory to processes, and handles virtual memory.
3. File System Management – Organizes data storage, file access, and directory structure.
4. Device Management – Controls hardware components like printers, keyboards, and storage devices.
5. Security & Access Control – Provides authentication, encryption, and protection against unauthorized access.
6. User Interface – Offers graphical (GUI) or command-line (CLI) interfaces for user interaction.

Types of Operating Systems:

• Batch OS – Executes batches of jobs with minimal user interaction.
• Time-Sharing OS – Allows multiple users to share system resources simultaneously.
• Distributed OS – Manages a network of computers, making them function as a single system.
• Real-Time OS (RTOS) – Processes data with minimal delay, used in critical applications like medical devices and automotive systems.
• Mobile OS – Designed for smartphones and tablets, such as Android and iOS.

Popular operating systems include Windows, macOS, Linux, and Unix for desktops, while Android and iOS dominate mobile devices.