Operating system

The operating system  (OS) is the most important program that runs on a computer. Every general-purpose computer must have an operating system to run other programs and applications .
Computer operating systems perform basic tasks, such as recognizing input from the keyboard , sending output to the display screen, keeping track of files and directories on the disk, and controlling peripheral devices  such as printers.
For large systems, the operating system has even greater responsibilities and powers. It is like a traffic cop — it makes sure that different programs and users  running at the same time do not interfere with each other. The operating system is also responsible for security , ensuring that unauthorized users do not access  the system.

Classification of Operating systems

-  Multi-user: Allows two or more users to run programs at the same time. Some operating systems permit hundreds or even thousands of concurrent users.

-  Multiprocessing : Supports running a program on more than one CPU.

-  Multitasking : Allows more than one program to run concurrently.

-  Multithreading : Allows different parts of a single program to run concurrently.

-  Real time: Responds to input instantly. General-purpose operating systems, such as DOS and UNIX are not real-time.

The three most popular types of operating systems for personal and business computing include Linux, Windows and Mac.

Linux Operating Systems

Linux is a freely distributed open source operating system that runs on a number of hardware platforms. The Linux kernel was developed mainly by Linus Torvalds and it is based on Unix.

Mac Operating Systems

Mac OS is the official name of the Apple Macintosh operating system . Mac OS features a graphical user interface (GUI) that utilizes windows, icons, and all applications that run on a Macintosh computer have a similar user interface.

Windows Operating Systems

Microsoft windows is a family of operating systems for personal and business computers. Windows dominates the personal computer world, offering a graphical user interface (GUI), virtual memory management, multitasking, and support for many peripheral devices.