为什么要学操作系统？

1. 会操作系统才会编程，浏览器、ide、病毒，是编程的“基础课”
2. 更多的研究方向

What is operating system？

Operating System: A body of software, in fact, that is responsible for making it easy to run programs (even allowing you to seemingly run many at the same time), allowing programs to share memory, enabling programs to interact with devices, and other fun stuff like that.

What is program？

程序就是状态机

那些普通的指令只能实现运算，甚至不能让程序停下来！

因此，syscall就是处理这些的

操作系统就是一系列API！