What is Operating System?
It is a software that works as an interface between a user and the computer hardware.
The primary objective of an operating system is to make computer system convenient to use and to utilize computer hardware in an efficient manner.
The operating system performs the basic tasks such as receiving input from the keyboard, processing instructions and sending output to the screen.
Major functions of operating systems may include:
1、Managing memory and other system resources.
2、Imposing security and access policies.
3、Scheduling and multiplexing processes and threads.
4、Launching and closing user programs, and providing basic system services for them.
5、Providing a basic user interface and application programmer interface.

And write sevral your familiar operating systems in details.

1、Microsoft Windows：
Microsoft Windows is a group of several graphical operating system families, all of which are developed, marketed and sold by Microsoft.
Each family caters to a certain sector of the computing industry. Active Microsoft Windows families include Windows NT and Windows IoT;
these may encompass subfamilies, e.g. Windows Server or Windows Embedded Compact (Windows CE).
Defunct Microsoft Windows families include Windows 9x, Windows Mobile and Windows Phone.
The development of Windows: Since Microsoft launched Windows 1.0 in 1985, Windows system has undergone more than ten years of change.
From Windows 3.0, which was originally run under DOS, to Windows XP, Windows 7, Windows 8 and recently released Windows 10, which are popular all over the world.
2、Mac OS：
The family of Macintosh operating systems developed by Apple Inc. includes the graphical user interface-based operating systems it has designed for use with its Macintosh series of personal computers since 1984, as well as the related system software it once created for compatible third-party systems.
The current Mac operating system is macOS, originally named \"Mac OS X\" until 2012 and then \"OS X\" until 2016.Developed between 1997 and 2001 after Apple\'s purchase of NeXT, Mac OS X brought an entirely new architecture based on NeXTSTEP, a Unix system, that eliminated many of the technical challenges that the classic Mac OS faced. The current macOS is preinstalled with every Mac and is updated annually. It is the basis of Apple\'s current system software for its other devices – iOS, watchOS, tvOS, and audioOS.
They share a common set of GUI principles, including a menu bar across the top of the screen; the Finder shell, featuring a desktop metaphor that represents files and applications using icons and relates concepts like directories and file deletion to real-world objects like folders and a trash can; and overlapping windows for multitasking.
3、Linux：
Linux is a family of open source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged in a Linux distribution.
Linux was originally developed for personal computers based on the Intel x86 architecture, but has since been ported to more platforms than any other operating system. Linux is the leading operating system on servers and other big iron systems such as mainframe computers, and the only OS used on TOP500 supercomputers (since November 2017, having gradually eliminated all competitors). It is used by around 2.3 percent of desktop computers. The Chromebook, which runs the Linux kernel-based Chrome OS, dominates the US K–12 education market and represents nearly 20 percent of sub-$300 notebook sales in the US.