Intro

Operating System

is a software that operates a computer system.

Computer

is a machine that processes the information.

Information

can be defined as a quantitative representation that measures the uncertainty.

• 정보의 최소 단위: bit(binary digit)

• 정보의 처리: 정보의 상태 변환 (0에서 1로, 1에서 0으로)

• 부울 대수(Boolean Algebra): NOT, AND, OR

• 논리 게이트: NOT, AND, OR, XOR, NAND, NOR

• 논리 회로 : IC, LSI, VLSI, ULSI, SoC, ..., 무어의 법칙, 황의 법칙

• 정보의 저장과 전송 : 플립-플롭, 데이터 버스

컴퓨터가 정보를 처리하는 방법

• 덧셈은? 반가산기, 전가산기

• 뺄셈은? 2의 보수 표현법

• 곱셈과 나눗셈은? 덧셈과 뺄셈의 반복

• 실수 연산은? 부동 소수점 표현법

• 함수는? GOTO

• 삼각함수, 미분, 적분, 사진 촬영, 동영상 재생 ...

컴퓨터의 범용성(Universality)

• NOT, AND, OR 게이트만으로 모든 계산을 할 수 있다.

• NAND 게이트만으로 모든 계산을 할 수 있다.

• 범용 컴퓨터(general-purpose computer)

컴퓨터의 계산가능성(Computability)

• Turing-computable: 튜링 머신으로 계산 가능한 것.

• 정지 문제(Halting Problem): 튜링 머신으로 풀 수 없는 문제

컴퓨터는 누가 만들었는가?

• 컴퓨터의 할아버지: Alan Turing-Turing Machine

• 컴퓨터의 아버지: John von Neumann-ISA: Instruction Set Architecture

앨런 튜링에 대해

현대 컴퓨터의 모형(CPU, RAM, Application Programs, Operating System)을 설계

1. Head와 Tape를 활용하여 목적성을 가진 Turing Machine을 만들 수 있음
2. Turing Machine을 엮어 Universal Turing Machine을 만들 수 있음
   

폰 노이만에 대해

명령을 끌어와서(fetch) 실행하는(execute) 사이클을 가진 내장형 프로그램 컴퓨터를 최초로 설계

A stored-program computer is a computer that stores programs in a memory.

Program

is a set of instructions that tells a computer's hardware to perform a task.

Operating System

• is a program running at all times on the computer

• to provide system services to application programs

• to manage processes, resources, user interfaces, and so on.

1.1 What Operating Systems Do

⭐ Operating system

• is a software that managers 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.

Computer system

can be divided roughly into four components

[1] hardware	[2] operating system	[3] application programs	[4] 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

1.2 Computer-System Organization

Classical Computer System

One or more CPUs and a number of device controllers connected through a common bus

⭐ Bootstrap Program

is the first program to run on computer power-on and then loads the operating system.

Interrupts

Hardware may trigger an 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 instruction in the instruction register.

The instruction is then decoded

• and may cause operands to be fetched from memory

• and stored in some internal register.

After the instruction on the operands

• has been executed,

• the result may be stored back in memory.

⭐ Storage System

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
* DMA(Direct Message Access)

1.3 Computer System Architecture

⭐ Definition of Computer System Components

1. CPU - The hardware that executes instructions.

2. Processor - A physical chip that contains on or more CPUs.

3. Core - The back computatino unit of the CPU.

4. Multicore - Including multiple computing cores on the same CPU.

5. 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

Muti-core design with several cores on the same processor chip.

⭐ Multiprogramming

1. runs more than one program at a time.

2. keeps several processes in memory simultaneously to increase CPU utilization.
   

Multiprogramming → Multitasking

is a logical extension of multiprogramming in which CPU switches jobs so frequently that users can interact with each job while it it running.

파워포인트 작업하면서 유튜브 동영상 시청할 때 CPU가 여러 작업을 빠르게 번갈아가며 수행하는데, 사용자는 이를 자연스러운 멀티태스킹으로 인지함.

⭐ CPU scheduling

If several processes are ready to run at the same time, the system must choose which process will run next.

1.4 Operating System Operations

⭐ User mode, Kernel mode

Two separate mode of operations to ensure that an incorrect program cannot cause other programs to execute incorrectly.
* 커널 모드 외에는 직접 하드웨어를 제어할 수 없기에 부적절한 명령이 방지됨.

⭐ 1.7 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, and so on.

* (a) a single operating system and (b) three virtual machines.

1.10 Computing Environments

Operating Systems in Variety of Computing Environments

1. Traditional Computing

2. Mobile Computing

3. Client-Server Computing (웹 클라이언트-서버 구조 etc)

4. Peer-to-peer Computing (음악/영화 공유, 토렌트 etc)

5. Cloud Computing (AWS, Azure, GCP etc)

▲ General Structure of a client-server system

▲ Peer-to-peer system with no centralized service

▲ Cloud Computing

2.1 Operating System Services

User Interface
Program execution
I/O operation
File-system manipulation
Communications
Error detection
Resource allocation
Logging
Protection and security

2.2 User and Operating - System Interface

Three fundamental ways for users to interface with the OS

1. CLI: command line interface, or command interpreter, known as shells, sh, bash, csh, tcsh, zsh, etc.

2. GUI: graphical user interface, Windows, Aqua for MacOS, KDE/GNOME for Linux, etc.

3. Touch-Screen Interface, Android UI, IPhone UI, etc.

2.3 System calls (aka. API of OS)

provides an interface to the services made available by the OS.

API(Application Programming Interface)

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

* printf (사용자가 open(), read(), write()하는 단계를 대신 함)

* Examples of Windows and UNIX system calls