operating_system.md

유저 모드: 하드웨어 접근이 안됨, 접근 시도 할 시, 익셉션이 발동함. 운영체제의 익셉션 핸들러 --> 커널모드로 변환됨.

cooperative approach: wait until a process makes a system call non-cooperative approach: os takes control

• problem: 해킹에 취약함, 프로그램에 버그가 있어도 컴퓨터가 먹통이 될 수 있음. Earlier versions of OSs used to take the cooperative approach.

interrupt: an unexpected event from outside the process exception: an unexpected even from within the process

timer interrupt: (intel) interrupt number 0.

context switch: written in assembly

scheduling:

• preemptive: can take cpu time from a running job
• non-preemptive: cannot take cpu time from a running job
  • sjf: smallest average turnaround time for a non-preemptive
    • problem: 간발의 차로 큰 job가 들어오면, 결국 다 늦어짐.

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starvation

• long running jobs never recieving any cpu time