LINUX System : Lecture 2 OS and UNIX summary Bong-Soo Sohn Assistant Professor School of Computer Science and Engineering Chung-Ang University Acknowledgement : (i) wikipedia.org, (ii)

Operating Systems OS acts as an intermediary between user and HW Resource Manager Allocates and manages system resources (CPU, Memory, Disks, Networks, … ) Efficient and fair use of the resources Interface OS allows users and application programs to access system resources Controls the execution of user programs accurately Efficiently, Fairly, Safely(Accurately), Abstractly

Computer System Structure HW – provides basic computing resources CPU, memory, disk (flash memory), … OS Kernel direct control of underlying HW System call Programming interface to the services provided by the OS The one program running at all times on the computer is the kernel. Everything else is either a system program (shipped with OS) or an application program Application programs Define the ways in which the system resources are used to solve user problems executed thru shell/GUI. Ex) word processor, video games, etc

Operating Systems Functionality Process Management CPU scheduling : batch vs time-sharing Memory Management Memory allocation : determine what is in memory when? Virtual memory : a technique that gives an application program the impression that it has large contiguous working memory, while in fact it is physically fragmented and may even overflow on to disk storage. Disk and file system Device driver : interface for communicating with HW devices Networking : supports network protocols. (ex) TCP/IP Security : authentication (login), authorization (file permission), … UI : GUI (Graphical User Interface), CLI (Command Line Interface) OS comes with application programs that provide an interface for managing OS.

Storage Hierarchy Register, Cache, Main memory, Secondary Storage (disks), Magnetic tapes Why hierarchical structure? Speed Cost Volatility Caching Copying information into faster storage system. Faster storage checked first to determine if information is there Cache main memory, main memory disk Important principle, performed at many levels in computer

OS Structures Multiprogramming a technique used to utilize maximum CPU time by running multiple programs Multiprogramming organizes jobs (code and data) so CPU always has one to execute One job is selected and run via job scheduler When a running job has to wait for I/O, OS switches to another job Multitasking (time-sharing) CPU switches jobs so frequently that users can interact with each job while it is running. Creates interactive computing Response time can be controlled If processes don’t fit in memory, swapping moves them in and out to run

Operating Systems MS Windows Most popular on desktop computers Gaining popularity in servers. UNIX/LINUX Most popular in server environments LINUX are gaining popularity on desktop PC.

UNIX History Created by Ken Thompson et al. ( a researcher at AT&T Bell Lab) UNICS(1969) (shortened to UNIX later) : first version (Assembly) Released Fifth version of UNIX kernel was rewritten in C, which was a big step forwards in terms of system portability (1973) EX) LINUX, FreeBSD, Solaris, AIX, HP-UX, IRIX, etc

UNIX-like OS

UNIX 장점 has been popular for more than two decades Portability (platform-independent) Written mostly in C + a few in assembly language Kernel size is small Multi-user, multi-tasking (interactive) environment Security (Permission) Stability Powerful networking capabilities (client-server model) LINUX is free / open source code Suitable for using as a server

UNIX 장점 UNIX is simple Clear design : 상대적으로 적은 개수의 system call Make each program do one thing well. (combined with pipe) Everything is file Uniform access to file, device and socket Written in C portability Fast process creation Various research (fork with COW) Robust IPC mechanism

LINUX Developed by Linus Torvalds( 핀란드 헬싱키대 ), in 1991 (22yo) Free open source UNIX OS for PC GPL license : GNU project by Richard Stallman 리눅스는 LINUX 커널 (Linus Torvalds) + LINUX 에서 실행되는 UNIX utilities/applications (GNU project) 로 구성됨 Now run on mainframe, supercomputer, embedded/smart system Open source code nature any one can add features and correct deficiencies. Turned into collaboration of volunteer developers around the world. Several different distributions (e.g. Redhat, Debian, … etc) a prepackaged kernel, system utilities, GUI, application programs Having all advantages of UNIX with low cost

LINUX Kernel Device driver support for various HW device Advanced processor and memory management Support different types of file system Shells / GUI : two forms of command input Textual command line shells (e.g. C shell, … ) Graphical user interface (e.g. GNOME window manager) System utilities Virtually every UNIX system utilities were ported to LINUX Include daemons server program running as a background process Application programs Come with standard application programs e.g. vi, emacs, xv, gcc/g++, xfig, latex, …

GPL (General Public License) GNU 에서 만든 free software license GNU GPL 이 적용된 SW 는 다음 사항을 강제함. 컴퓨터 프로그램을 어떠한 목적으로든지 사용할 수 있다. 다만 법 으로 제한하는 행위는 할 수 없다. 컴퓨터 프로그램의 실행 복사본은 언제나 프로그램의 소스 코드 와 함께 판매하거나 소스코드를 무료로 배포해야 한다. 컴퓨터 프로그램의 소스 코드를 용도에 따라 변경할 수 있다. 변경된 컴퓨터 프로그램 역시 프로그램의 소스 코드를 반드시 공 개 배포해야 한다. 변경된 컴퓨터 프로그램 역시 반드시 똑같은 라이선스를 취해야 한다. 즉 GPL 라이선스를 적용해야 한다.