Operating System Services
- OS provides an environment for the execution of programs.
User and Operating-System Interface
- CLI - shells
- GUI
- Touch-Screen Interface
System Calls
- provide an interface to the services made available by the OS.
- OS에서 서비스가 사용가능하도록 하기 위해 제공하는 인터페이스
- user mode 와 kernel mode를 넘나들며 수행됨