Operating System Introduction

운영체제란

• An operating system is a software that operates a computer system.
• A computer is a machine that processes the information.
• An information can be defined as a quantitative representation that measures the *uncertaint

컴퓨터의 정보 처리

• 정보의 최소 단위: bit(binary digit)
• 정보의 처리: 정보의 상태 변환 (0 -> 1 or 1 -> 0)
• Boolean Algebra: NOT, AND, OR
• 논리 게이트: NOT, AND, OR, XOR, NAND, NOR
• 논리회로: IC, LSI, SoC, ...
  • Moore's law
• 정보의 저장과 전송: Flip-Flop, Data Bus

컴퓨터의 연산 처리 방식

• 덧셈: 반가산기, 전가산기
• 뺄셈: 2의 보수 표현법
• 곱셈 & 나눗셈: 덧셈과 뺼셈의 반복
• 실수 연산: 부동 소수점
• 함수: GOTO
• 이를 기반으로 다양한 작업을 수행

컴퓨터는 다음 조건을 충족해야 한다

• Universality(범용성)

  • NOT, AND, OR 게이트만으로 모든 계산을 할 수 있다.
  • NAND 게이트만으로 모든 계산을 할 수 있다.
  • General-purpose computer(범용 컴퓨터)

• Computability(계산가능성)

  • Turing-computable: 튜링 머신으로 계산가능한 것.
  • Halting Problem: 튜링 머신으로 풀 수 없는 문제.

컴퓨터의 탄생

• Alan Turing - Turing Machine
• John von Neumann - ISA(Instruction Set Architecture)

Turing Machine

• Alan Turing이 현대 컴퓨터의 원형을 제시함

ISA

• Neumann이 stored-program 방식을 처음으로 제시
  • A stored-program computer is a computer that stores programs in a memory.
  • Memory에서 Instruction을 fetch를 해오고 CPU에서 Execute하는 구조

• 따라서, a program is a set of instructions that tells a computer's hardware to perform a task.

운영체제도 프로그램의 일종

• Operating System
  • is a program running at all times on the computer
  • to provide system services to application programs
  • to manage process, resources, user interfaces, and so on.

What Operating Systems Do

• An OS 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.

Four components of computer system

• The hardware
• The OS
• The application programs
• And a user

Defining Operating Systems

• There are NO universally accepted definition of an operating system.
• A 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

Computer-System Organization

• A modern computer system consist of
  • one or more CPUs and
  • a number of device controllers connected through a common bus.

Bootstrap

A bootstrap program is the first program to run on computer power-on, and then loads the OS.

Interrupt

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

von Neumann architecture

• A typical instruction-execution cycle
  • first fetches an instruction from memory
  • and stores that instrcution in the instruction register.
• The instrcution is then decoded
  • and may cause operands to be fetched from memory
  • and stored in some internal register.
• After then instruction on the operands
  • has been executed,
  • the result may be stored back in memory.

Storage systems

The wide variety of storage systems can be organized in a hierarchy according to

• storage capacity
• and access time

I/O Structure

A large portion of OS code is dedicated to managing I/O

Computer System Architecture

• Definitions of Computer System Components
  • CPU: The hardware that executes instructions
  • Processor: A physical chip that contains one or more CPUs.
  • Core: The back computation unit of the CPU.
  • Multicore: Including multiple computing cores on the same CPU.
  • Multiprocessor: Including multiple processors.

Symmetric multiprocessing (SMP)

• The most common multiprocessor systems, in which each peer CPU processor performs all tasks.
• Asymmetric multiprocessing: each processor is assigned a specific task.

Multi-core design

• With several cores on the same processor chip.

Operating System Operations

Multiprogramming

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

Multiprocessing (=multitasking)

• a logical extension of multiprogramming.
  • in which CPU switched 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.

User mode & Kernel mode

• Two separate mode of operations: user mode and kernel mode to ensure that an incorrect program.
  • cannot cause other programs to execute incorrectly

Virtualization

• Virtualization is a technology that allow us
  • to abstract the hardware of a single computer
  • into several different execution environments.
• VMM: Virtual Machine Manager
  • VMware, XEN, WSL, ...

Operating System Services

• OS provides an environment for the execution of programs.
  • User interface
  • Program execution
  • I/O operation
  • File-system manipulation
  • Communications
  • Error detection
  • Resource allocation
  • Logging
  • Protection and securit

User and Operating System Interface

• Three fundamental ways for users to interface with the OS
  • CLI: command line interface, or command interpreter
    • known an shells: sh, bash, csh, tcsh, zsh, etc
  • GUI: graphical user interface
    • Windows, Aqua for MacOS, KDE/GNOME for Linux, etc
  • Touch-Screen Interface
    • Android UI, iPhone UI, etc

System calls

• System calls provides an interface to the services made available by the OS
• API: Application Programming Interface