Operating System

An Operating System (OS) is system software that manages computer hardware, software resources, and provides various services for computer programs. It acts as an intermediary between the computer hardware and the user applications. 

The primary functions of an operating system include:

1. Process Management: The OS manages processes, which are instances of executing computer programs. This includes process scheduling, creation, termination, and communication between processes.
2. Memory Management: The OS is responsible for managing the computer's memory, ensuring that each process has the necessary memory space for execution and preventing one process from interfering with another.
3. File System Management: Operating systems provide a file system that organizes and stores data on storage devices. This includes file creation, deletion, and manipulation, as well as managing directories and file permissions.
4. Device Management: The OS facilitates communication between software and hardware components. It manages device drivers, which are software interfaces to hardware devices, allowing programs to interact with peripherals like printers, disk drives, and network interfaces.
5. Security and Protection: Operating systems implement security measures to protect the system and its data from unauthorized access and malicious software. This includes user authentication, access controls, and encryption.
6. User Interface: Operating systems provide a user interface that allows users to interact with the computer. This can be a command-line interface (CLI), graphical user interface (GUI), or a combination of both.
7. Networking: Many modern operating systems include networking capabilities to enable communication between computers in a network. This includes protocols for data transmission, network configuration, and internet connectivity.

There are various types of operating systems, including:

1. Single-user, Single-tasking: Examples include MS-DOS.
2. Single-user, Multi-tasking: Examples include Microsoft Windows, macOS.
3. Multi-user: Examples include Unix, Linux.
4. Real-time Operating Systems (RTOS): Used in embedded systems and applications where response time is crucial, such as in control systems and robotics.
5. Mobile Operating Systems: Examples include Android, iOS.

Popular operating systems as of my last knowledge update in January 2022 include Microsoft Windows, macOS, Linux distributions (such as Ubuntu, Fedora, and Debian), Android, and iOS. The landscape may have evolved since then.