02. 운영체제의 개념과 구조: Chapter 1-2. Introduction & O/S structures.

An operating system is

• a software that manages a computer ‘s hardware
• It also provides a basis for application programs and
  • acts as an intermediary between
  • the computer user and the computer hardware → 유저와 하드웨어의 매개 역할
    

Computer system can be divided roughly into four components

1. Hardware
2. Operating System
3. Application Programs
4. User

Defining Operating Systems

• 통상적으로 정의되지 않았음.
• More common definition is that
  • “the one program running at all times on the computer”
  • usually called the kernel
    → Along with the kernel, there are two other types of programs
  • system programs
  • application programs

What is bootstrap(부팅)?

• RAM은 휘발성이므로 ROM에 O/S 프로그램 존재

1. the first program to run on computer power-on,
2. loads the O/S
   
   

Interrupts

• Hardware may trigger an interrupt at any time → by sending a signal to the CPU, usually by way of the system bus
  

Storage systems

• Storage systems can be organized in a hierarchy according to: → storage capacity, and access time : 그림의 위쪽이 속도가 빠르고, 블록의 크기는 용량에 비례한다.
  

I/O Structure

• DMA(Directed Memory Access) : CPU의 개입 없이 I/O 장치와 Memory 사이의 데이터를 전송하는 접근방식

  

  
  

Symmetric multiprocessing(SMP)

• The most common multiprocessor systems
  • in which each peer CPU processor performs all tasks.

Multi-core design

• with several cores on the same processor chip

Multi programming

• runs more than one program at a time
• keeps several processes in memory simultaneously
• to increase CPU utilization

Multitasking(multiprocessing) [Concurrent]

• logical extension of multi programming
  • in which CPU switches jobs so frequently that
  • users can interact with each job while it is running
• CPU scheduling
  - If several processes are ready to run at the same time
  - the system must choose which process will run next
  
  

Two separate mode of operations

• User mode and Kernel mode
• to ensure that an incorrect program
  • cannot cause other programs to execute incorrectly

Virtualization(가상화)

• a technology that allow us
  • to abstract the hardware of a single computer
  • into several different execution environments
• VMM(Vertual Machine Manager) → 동시에 O/S를 여러개 실행 가능
  • VMware, XEN, WSL…

A computer running(a) a single O/S and (b) three virtual machines

OS provides an environment for the execution of programs

• User interface
• Program execution
• I/O operation
• File-system manipulation(파일 조작)
• Communications
• Error detection
• Resource allocation(자원 할당)
• Logging
• Protection and security

가장 중요한 것은 Process, thread. → multiprocessing(CPU-scheduling) → synchronization → deadlock

⇒ memory management → virtual memory management …

A view of O/S services

Three fundamental ways for “users” to interface with OS

• CLI : command line interface, or command interpreter
  • known as shells : sh, bash, csh, tcsh, zsh…
• GUI : graphical user interface(can use mouse)
  • Windows, Aqua for MacOS, KDE/GNOME for Linux…
• Touch-Screen Interface
  • Android UI, iPhone UI…

How can programs interface with OS? [System calls]

• provide an interface to the services made available by the OS
• API : Application Programming Interface

So, API of OS is “System call”

The handling of a user application invoking the open() system call

참고 :

Silberschatz et al. 『Operating System Concepts』. WILEY, 2020.

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