Download LINUX System (English

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) http://www.doc.ic.ac.uk/~wjk/UnixIntro
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, …
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


Memory Management








CPU scheduling : batch vs time-sharing
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 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
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 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
 Stability
 Powerful networking capabilities
 Free, open source code(LINUX)
Suitable for using as a server
UNIX History

Created by Ken Thompson et al. ( a researcher at AT&T Bell Lab)
 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




Shells / GUI : two forms of command input



Device driver support for various HW device
Advanced processor and memory management
Support different types of file system
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, …