What is Process?

• A process is a program in execution - 실행중인 프로그램
  • Shell, 혹은 GUI에서 프로그램을 실행시키면, 저장장치에서 memory로 프로그램이 올라가게 된다. 이를 실행중인 프로그램 즉, 프로세스라고 한다.
• Unit of work in an operating system
• Process will need certain resources to accomplish its task
  • CPU time, memory, files, I/O devices

The memory layout of a process is divided into multiple sections

1. Text section : the executable code

2. Data section : global variables

3. Heap section : memory that is dynamically allocated during program run time

   (프로그램이 실행되는 동안 동적으로 할당된 메모리)

4. Stack section

   1. temporary data storage when invoking functions

      (함수 호출 시 임시 데이터 저장공간)

   2. such as function parameters, return addresses, and local variables

Layout of a process in memory

Diagram of Program and Process

As a process executes, it changes its “state”

• New : the process is being created

• Running : Instructions are being executed

  ****(프로그램을 실행시켜 CPU가 명령어를 실행할 준비가 된 상태)

• Waiting : the process is waiting for some event to occur

  • such as an I/O completion or reception of a signal (다른 프로세스를 실행중인 경우 waiting)

• Ready : the process is waiting to be assigned to a processor

  (프로세스가 프로세서에 할당되기를 기다리는 상태. 다른 프로세스를 종료해도 바로 프로세서를 점유 하지 못함.)