1. UNIX OPERATING
SYSTEM
BY:251,253,254,252,255

2. In-order to introduce
concept of UNIX O.S we should go
through certain topics :
1-> COMPONENTS OF COMPUTER SYSTEM.
2-> WHAT IS AN OPERATING SYSTEM ?

3. End
User
Programmer
Operating-
System
Designer
Computer Hardware
Operating-System
Utilities
Application
Programs

4. Hardware – provides basic computing resources (CPU, memory, I/O
devices).
Operating system – controls and coordinates the use of the hardware
among the various application programs for the various users.
Utilities – Programs that assist in system management and software
development.
Applications programs – define the ways in which the system
resources are used to solve the computing problems of the users
(compilers, database systems, video games, business programs).

5. An Operating System is a program that acts as an
interface between the user of a computer and the
computer hardware.
Operating system goals:
* Control/execute application programs.
* Make the computer system convenient to use.
* Make solving user problems easier.
* Use the computer hardware in an efficient manner.

6. The Unix operating system found its beginnings in MULTICS
which stands for Multiplexed Operating and Computing
system.
The MULTICS project began in the mid 1960s as a joint effort
by General Electric, Massachusetts Institute for
Technology and Bell Laboratories.
In 1969 Bell Laboratories pulled out of the project.

7. One of Bell Laboratories people
involved in the project
was “Ken Thompson”.
He liked the potential MULTICS had, but felt it was too
complex and that the same thing could be done in simpler
way.
IN 1969 he wrote first version of UNIX called as UNIC.
UNICS stood for “UNI-PLEXED” operating system
And eventually shortened to UNIX.

9. Kernel: The kernel is the heart of the operating system. It interacts
with hardware and most of the tasks .
Shell: The shell is the utility that processes your requests. When you
type in a command at your terminal, the shell interprets the command
and calls the program that you want.
Commands and Utilities: There are various command and
utilities which you would use in your day to day activities. cp,
mv, cat and grep.
Files and Directories: All data in UNIX is organized into files. All
files are organized into directories. These directories are organized
into a tree-like structure called the file system.

10. 1. Multi-user system : Multi-user capability of UNIX allows several users to
use the same computer to perform their tasks.
2. Multi-tasking : Multitasking is the capability of the operating system to
perform various task simultaneously, i.e. a user can run multiple tasks
concurrently.
3. Programming Facility : UNIX is highly programmable, the UNIX shell
has all the necessary ingredients like conditional and control structures, etc.

11. 4. Security : UNIX allows sharing of data; every user must have a single
login name and password. So, accessing another user’s data is impossible
without his permission.
5. Portability : UNIX is portable because it is written in a high level
language. So , UNIX can be run on different computers.

12. RAM – 256 MB .
HARD DRIVE – 10 minimum and maximum depends on the user
requirement.
VIDEO– Minimum 800X600.
MOUSE – Any.
REMOVAL MEDIA – Most SCSI.
PRINTER – Almost any parallel or serial port.
MODEM– Most serial, if DOS can use it, Unix can too……..
NIC – 3Com, Novell, HP, Intel - Clones are NOT recommended.

13.  UNIX is a multitasking system.
 Multiple programs can be executed at the same time.
 Ultimately, a program needs to be executed by a CPU.
 If there is only one CPU, how multiple programs can be executed
at the same time?
By time sharing
 That is, all programs are claimed to be executing. In fact, most of
them are waiting for the CPU.

14.  A program that is claimed to be executing is called a process.
 For a multitasking system, a process has at least the following three
states:

15.  Ready state
 All processes that are ready to execute but without the CPU are
at the ready state
 If there is only 1 CPU in the system, all processes except one
are at the ready state
 Running state
 The process that actually possesses the CPU is at the running
state
 If there is only 1 CPU in the system, at most there is only one
process is at the running state
 Sleeping state
 The process that is waiting for other resources, e.g. I/O, is at the
sleeping state

16.  Processes will alternatively get into the CPU one after the other
(called the round robin scheme)
 A process will be “in” a CPU for a very short time (quantum)
 For Linux, each quantum is about 100msec
 At the time that a process is selected to be “in” the CPU
 It goes from ready state to running state
 After that, it will be swapped out
 It goes from running state back to ready state
 Or it may due to the waiting of an I/O device, e.g. mouse
 It goes from running state to sleeping state
 When obtaining the required resource
 It goes from sleeping state to ready state

17. WHAT IS MEMORY ?
Primary memory is a precious resource that frequently cannot contain all
active processes in the system.
WHAT IS MEMORY MANAGEMENT ?
The memory management system decides which processes should reside
(at least partially) in main memory
It monitors the amount of available primary memory and may periodically
write processes to a secondary device called the swap device to provide
more space in primary memory.

18. FIG : Typical internal memory layout for single user-
memory part UNIX

19. MEMORY MANAGEMENT CONCEPTS OF UNIX
1.SWAPPING .
The swap device is a block device in a configurable section of a disk
Kernel allocates contiguous space on the swap device without
fragmentation
It maintains free space of the swap device in an in-core table, called
map
The kernel treats each unit of the swap map as group of disk blocks
As kernel allocates and frees resources, it updates the map
accordingly

20. 2. DEMAND PAGING.
Not all page of process resides in memory locality.
When a process accesses a page that is not part of its working set, it incurs a page
fault.
The kernel suspends the execution of the process until it reads the page into memory
and makes it accessible to the process.
OTHER TECHNIQUES USED ARE AS FOLLOWS
1.Allocating swap space .
2.Free space swap.
3.Page table entry.
4.Disk block description..

21. A file system is a logical collection of files on a partition or disk.
A partition is a container for information and can span an entire hard drive if desired.
Everything in Unix is considered to be a file, including physical devices such as DVD-ROMs,
USB devices, floppy drives, and so forth.

22. Unix uses a hierarchical file system structure, much like an upside-
down tree, with root (/) at the base of the file system
and all other directories spreading from there.
It has a root directory (/) that contains other files and directories.
Each file or directory is uniquely identified by its name, the
directory in which it resides, and a unique identifier ,typically called
an inode.
It is self contained. There are no dependencies between one file
system and any other.
The directories have specific purposes and generally hold the
same types of information for easily locating files.
Following are the directories that exist on the major versions of
Unix:

23.  The directories have specific purposes and generally
hold the same types of information for easily locating
files.
 It has a root directory (/) that contains other files and
directories.
 The inode type field distinguishes between plain files and
directories
 Directory entries are of variable length; each entry
contains first the length of the entry, then the file name
and the inode number

24. (/mnt) Used to mount other temporary file systems, such as cd rom and
floppy for the CD-ROM drive and floppy disks
(/proc) Contains all processes marked as a file by process number or
other information that is dynamic tot he system.
(/tmp) Holds temporary files used between system boots.
(/usr) Used for miscellaneous purposes, or can be used by many users.
Includes administrative commands, shared files , library files.
(/var ) Typically contains variable-length files such as log and print
files any other type of file that may contain a variable amount of
(/sbin) Contains binary (executable) files, usually for system
administration. For example f-disk and if-config utilities.
(/kernel)Contains kernel files

25. Being a multi-user system - UNIX have a tremendous amount of
security to offer; many being open source, which can be validated and
modified to meet anyone’s needs.
UNIX system security can be divided into three main areas of concern.
Two of these areas, account security , file system security,
Network security.

26. Before , any advanced system we should provide physical security to system by keeping it in a
secure and protected area to avoid unauthorized access.
ACCOUNT SECRITY:
 UNIX user community haves no. of user who are given acces to system using authorized (UID) &
(GID).
 The access codes (passwords) to (UID) & (GID) are stored in system
as stored in encrypted format SALTED PASSWORDS to avoid
cracking of pswd.
EX:
UID : syslog 56
Password :**********
The same information is stored in system files in following format:
UID:SaltID:Saltedhash:EncrypedPassword:UserID:GroupID:Complete_Name:home_dir:shell_bin

27. FILE SYSTEM SECURITY.
 File system security is about making sure your users can only do what you want them
to be able to do. This means that you want system programs to be secure and users
to only be able to write where you want them to be able to.
 To impliment this uses tecn. OF ACLs PERMISSIONS.
 Almost modern files systems, include ACLs to give unprivileged access to only
certain users.

 Permissions are separated by owner, group, and others. On UNIX systems
permissions are displayed as rwxrwxrwx
 With a few more special settings, Desktop environments also provide GUI settings for
easy modifying

28. NETWORK SECURITY
 Once you put a computer on a network, you allow many more people
potential access to the machine. The key to network security is to allow only
those functions that the users actually need. By disabling non-used
functions, you have much less monitoring/securing.
 Telnet Security:
Using SSH (secure shell). SSH provides encrypted traffic to prevent
snooping.
 FTP Security:
As with other services, if you do not need this functionality, turn it off.
You can turn off incoming FTP or simply certain users. If you need
full FTP functionality, be certain to enable logging and monitor
syslog.

29. TO GET A CONCLUSION TO OUR PRESENTATION WE ARE PUTTING
FORWARD A COMAPRISON OF WINDOWS OS & UNIX OS.
1.As far as operating systems go, to some it would seem as if UNIX has a
clear advantage over Windows. UNIX offers greater flexibility than Windows
operating systems and it is more stable .
FEW AREAS OF COMPARISON :-
 BETTER MULTIUSER APPROACH.
 BETTER PROCESS HEIRARCHY.
 USE OF DAEMONS.
 BETTER PROGRAMMING ENVIORMENT.

30. OTHER PRACTICAL COMPARISON WOULD BE :
 Cost
 User
 Security
 Processors
 Multiprocessing
 Open source
 File system supported
So we can say UNIX far more better
Than WINDOWS .