Single-User Operating Systems

Introduction:
An operating system (OS) serves as the interface between a user and the computer hardware. It manages computer resources, provides essential services, and allows users to execute programs. Operating systems can be categorized based on various factors, such as the number of users they support. Single-user operating systems are designed to be used by a single user at a time, while multi-user operating systems can handle multiple users concurrently.

Options:
The given options are:
a) DOS
b) Unix
c) Linux
d) Windows

Explanation:
Out of the given options, the single-user operating system is:
a) DOS (Disk Operating System)

1. DOS (Disk Operating System):
- DOS is an early operating system primarily used with IBM-compatible personal computers.
- It was developed by Microsoft and was widely used during the 1980s and early 1990s.
- DOS is a single-user operating system, meaning it allows only one user to access the system at a time.
- It does not support concurrent multi-user access or provide built-in user management features.
- DOS primarily provides a command-line interface (CLI) for users to interact with the system.
- It lacks advanced features and does not have built-in support for multitasking or multi-threading.
- DOS is known for its simplicity and compatibility with a wide range of hardware and software.

2. Unix:
- Unix is a multi-user operating system developed in the 1970s.
- It was designed to support multiple users accessing the system simultaneously.
- Unix provides robust user management features, allowing multiple users to have their accounts and permissions.
- It supports multitasking, multi-threading, and provides a command-line interface.
- Unix has been highly influential and has served as the foundation for various operating systems, including Linux and macOS.

3. Linux:
- Linux is a free and open-source operating system developed based on Unix.
- Like Unix, Linux is designed to support multiple users concurrently.
- It provides robust user management, multi-tasking, and multi-threading capabilities.
- Linux offers a variety of graphical user interfaces (GUIs) in addition to the command-line interface.
- It is widely used in servers, embedded systems, and desktop computers.

4. Windows:
- Windows is a popular operating system developed by Microsoft.
- It is primarily designed for personal computers and supports multiple users.
- Windows provides a graphical user interface (GUI) and supports multi-tasking and multi-threading.
- It offers various editions, including ones for home users and enterprise environments.

Therefore, based on the given options, the single-user operating system is DOS.