An operating system (OS) is system software that manages hardware resources and provides a platform for applications to run. Without an OS, programs cannot interact with hardware like CPU, memory, storage, or input/output devices.

Functions of an Operating System:

Process Management:
Handles creating, scheduling, and terminating processes.

Memory Management:
Allocates RAM to programs and ensures safe, efficient usage.

File System Management:
Manages files, directories, storage access, and permissions.

Device Management:
Coordinates communication between hardware devices and drivers.

Security & Access Control:
Protects data, manages user permissions, and enforces system policies.

User Interface:
Provides CLI or GUI for users to interact with the system.

In short:
An operating system acts as the core controller that enables hardware and software to work together efficiently and securely.