Chapter 1 Introduction
What is an operating system：3个
一intermediary between user and hardware
二Resource allocator: manage 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
Two types of interrupt handling
一polling: cpu为主动，定期向外围设备发