리눅스 : Lecture 2 운영체제 및 UNIX 요약 중앙대학교 컴퓨터공학부 손 봉 수 교수

Operating Systems OS 는 사용자와 HW 간의 중간 매개체 역할을 한다. 자원 관리자 (Resource Manager) 시스템 자원 (CPU, Memory, Disks, Networks) 을 할당하고 관리함. 자원의 효율적이고 공정한 사용을 목표로 함. 인터페이스 (Interface) OS 는 사용자와 응용프로그램이 시스템 자원에 접근하고 사용할수 있도록 함. 사용자 프로그램의 실행을 제어함. 효율성, 공정성, 정확성, 추상성 (abstract) 지향

Computer System Structure HW – 기본적인 computing resources 제공 CPU, memory, disk, … OS 커널 (Kernel) HW 를 직접 제어 System call 시스템 자원에 대하여 OS 에 의해 제공되는 서비스가 일종의 함수 형태로 되어있는 programming interface 커널은 전원이 켜져있는 컴퓨터에서 항상 실행되고 있다. 다른 프로그램은 OS 와 함께 제공되는 시스템 프로그램 (system program) 이거나 응용 프로그램 (application program) 이다. 응용 프로그램 (Application programs) 시스템 자원이 사용자의 문제를 해결하는데 사용되는 방 식을 정의함. 쉘 또는 GUI 를 통해 실행됨 Ex) 워드프로세서, 컴퓨터 게임 등

Operating Systems 운영체제의 기능 프로세스 관리 (Process Management) CPU scheduling : batch vs time-sharing 메모리 관리 (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 제공 및 관리 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)

저장 장치의 계층 (Storage Hierarchy) Register, Cache, Main memory, Secondary Storage (disks), Magnetic tapes Why hierarchical structure? Speed Cost 휘발성 (Volatility) 캐슁 기법 (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

멀티프로그래밍, 시분할 멀티프로그래밍 (Multiprogramming) a technique used to utilize maximum CPU time by running multiple programs simultanously Single user cannot keep CPU and I/O devices busy at all times. 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 시분할 (time-sharing) 시스템 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 System has been popular for more than two decades Portability Written mostly in C + a few in assembly language Kernel size is small Multi-user, multi-tasking environment 안정성 (Stability) Powerful networking capabilities Free, open source code(LINUX) Suitable for using as a server

UNIX History Ken Thompson et al. (AT&T Bell Lab 연구원 ) 이 만듬 UNICS(1969) (shortened to UNIX later) : first version Released Fifth version of UNIX kernel was rewritten in C, which was a big step forwards in terms of system portability (1973) LINUX Developed by Linus Torvalds, a finnish undergrad student, in 1991 Free open source UNIX OS for PC Open source code nature means any one can add features and correct deficiencies. Turned in to collaboration of hundreds of volunteer developers around the world. Several different distributions (e.g. Redhat, Debian, … etc) Distribution comprises a prepackaged kernel, system utilities, GUI, application programs

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, …