1. Program vs. Process
   Program are things your write
   Process is the instance of the program that is running.
   Software load to Memory, Processor assign register to Memory, Program become executing entity(process)
2. Context Switch
   Processor change working things rapidly, give you a sense that running multiple things at the same time
3. Scheduling, Protection
   Scheduling: Which process use processor
   (can be fair share, but when there are lot of process, things will be slow)
   Protection: Prevent cross flow of information
4. I/O
   Providing a virtual abstraction of the devices to the processes that are running
   (43%-50% 的crash 是由Device Driver 導致的，因為它的開發是由第三方完成，而不是OS writer， quality 不一定好)

TextBook:
https://download.csdn.net/download/qq_39412935/10842898