1.

An operating system acts as an intermediary between the user of acomputer and the computer hardware. The purpose of an operatingsystem is to provide an environment in which a user can executeprograms in a convenient and efficient manner.
An operating system is software that manages the computer hard-ware. The hardware must provide appropriate mechanisms to ensure thecorrect operation of the computer system and to prevent user programsfrom interfering with the proper operation of the system.

2.

A. Windows：Windows is the most common computer operating system. It is the operating software developed by Microsoft. The software has experienced many years of development, the current launch of the win10 system is quite mature. The Windows operating system has the characteristics of good man-machine interaction, many supporting applications and strong hardware adaptability.

B. Mac：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. Mac system is a graphical operating system based on Unix kernel. An operating system that cannot normally be installed on a regular PC. Developed by apple itself. The system is very reliable; Many of its features and services embody apple's philosophy.In addition, most of the computer viruses that have gone viral are targeted at Windows, and because the MAC has a different architecture from Windows, it is rarely attacked by viruses. The macOS interface is unique, highlighting iconic ICONS and human-computer conversations.