1.What is Operating System?

Operating system is a computer program that manages computer hardware and software resources, and is also the core and cornerstone of computer system.The main functions of operating system are to manage and configure memory, determine the priority of system resources supply and demand, control input and output devices, operate network and manage file system. The operating system also provides an interface for users to interact with the system. Linux Linux is a set of free-to-use and free-to-spread Unix-like operating system. It is a multi-user, multi-task, multi-threaded and multi-CPU operating system based on POSIX and UNIX.

2.Write sevral your familiar operating systems in details.

Microsoft Windows：Microsoft Windows operating system is a set of operating system developed by Microsoft in the United States, which was published in 1985.Windows USES a graphical GUI, which is more user-friendly than the way DOS used to require typing instructions.

Linux：Linux is a set of free use and free dissemination of unix-like operating system, is a POSIX and unix-based multi-user, multi-task, support multi-threading and multi-cpu operating system.It can run major UNIX tools, applications, and network protocols.

Android：Android is a free and open source operating system based on Linux.Mainly used in mobile devices, such as smartphones and tablets, led and developed by Google (Google) and the open handset alliance.

IOS：IOS is a mobile operating system developed by apple.The system was first unveiled by Apple at the Macworld conference on January 9, 2007. It was originally designed for the iPhone and has since been applied to products such as the iPod touch, iPad and Apple TV.

Mac OS：Mac OS is an operating system that runs on apple\'s Macintosh computers.Mac OS was the first successful graphical user interface operating system in the commercial world.The latest version available is macOS 10.14.4, and there is also a Mac system running on PCS on the web, called Mac PC.