Chapter 1 Introduction
? What is an operating system：3个
一intermediary between user and hardware
二Resource allocator: acts as the manager all resources、decide between conflicting requests for efficient and fair resource use(例子：打印机)
三control program: control excution of programs to prevent errors and improper use of computer（例子：C语言编程指针访问）
? 4components of computer systems:
The hardware ,the operating system, the application system(应用系