Linux operating system

2.  The Unix operating system is a set of programs that act
as a link between the computer and the user.
 Unix was originally developed in 1969 by a group of
AT&T employees Ken Thompson, Dennis Ritchie,
Douglas McIlroy, and Joe Ossanna at Bell Labs.
 There are various Unix variants available in the
market. Solaris Unix, AIX, HP Unix and BSD are a few
examples. Linux is also a flavor of Unix which is freely
available.

3.  Several people can use a Unix computer at the
same time; hence Unix is called a multiuser
system.
 A user can also run multiple programs at the same
time; hence Unix is a multitasking environment.

4. Users communicate with the kernel through a
program known as the shell. The shell is a
command line interpreter; it translates commands
entered by the user and converts them into a
language that is understood by the kernel.

5. Fig: Unix
Architecture

6. The kernel is the heart of the operating system. It
interacts with the hardware and most of the tasks like
memory management, task scheduling and file
management.
SOME OTHER FUNCTIONS PERFORMED BY THE
KERNEL IN UNIX SYSTEM ARE:
Managing the machine’s memory and allocating it to each
process and decides their priorities.
Scheduling the work done by the CPU so that the work of
each user is carried out as efficiently as is possible.

7.  Organizing the transfer of data from one part of
the machine to another.
 Accepting instructions from the unix shell and
carrying them out.
 Enforcing the access permissions that are in force
on the file system

8. 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. The shell uses standard syntax for all commands. C
Shell, Bourne Shell and Korn Shell are the most famous
shells which are available with most of the Unix variants.

9.  You can use any one of these unix shells if they are
available on your system. And you can switch
between the different unix shells once you have
found out if they are available.
TC shell (tcsh)
Korn shell (ksh)
Bourne Again SHell (bash)
Bourne shell (sh)
C shell (csh)

10. There are various commands and utilities which you can
make use of in your day to day activities. cp, mv,
cat and grep, etc. are few examples of commands and
utilities. There are over 250 standard commands plus
numerous others provided through 3rd party software.
All the commands come along with various options.

11. All the data of Unix is organized into files. All files are
then organized into directories. These directories are
further organized into a tree-like structure called the
files ystem.

12. 1. Security
The operating system uses password protection to protect
user data and similar other techniques. it also prevents
unauthorized access to programs and user data.
2. Control over system performance
Monitors overall system health to help improve performance.
records the response time between service requests and
system response to have a complete view of the system
health. This can help improve performance by providing
important information needed to troubleshoot
problems.

13. 3. Job accounting
Operating system Keeps track of time and resources used by
various tasks and users, this information can be used to
track resource usage for a particular user or group of user.
4. Error detecting aids
Operating system constantly monitors the system to detect
errors and avoid the malfunctioning of computer system.

14. 5.Coordination between other software and users
Operating systems also coordinate and assign interpreters,
compilers, assemblers and other software to the various
users of the computer systems.
6.Memory Management
The operating system manages the Primary Memory or Main
Memory. Main memory is made up of a large array of bytes
or words where each byte or word is assigned a certain
address. Main memory is a fast storage and it can be
accessed directly by the CPU. For a program to be executed,
it should be first loaded in the main memory.

15. 7. Processor Management
In a multi programming environment, the OS decides the
order in which processes have access to the processor, and
how much processing time each process has. This
function of OS is called process scheduling. An Operating
System performs the following activities for processor
management.
8. Device Management
An OS manages device communication via their respective
drivers. It performs the following activities for device
management. Keeps tracks of all devices connected to
system. designates a program responsible for every device
known as the Input/Output controller.

16. 9. File Management
A file system is organized into directories for efficient or
easy navigation and usage. These directories may contain
other directories and other files. An Operating System
carries out the following file management activities. It
keeps track of where information is stored, user access
settings and status of every file and more… These facilities
are collectively known as the file system.

18. a) Hardware layer − Hardware consists of all
peripheral devices (RAM/ HDD/ CPU etc).
b) Kernel − It is the core component of Operating
System, interacts directly with hardware, provides
low level services to upper layer components.
c) Shell − It takes commands from the user and
executes kernel's functions.
d) Utilities − Utility programs that provide the user
most of the functionalities of an operating systems.

19. ⚫It interacts with the actual hardware in machine
language.
⚫It is the monarch who has overall control of
everything.
⚫ It has various functions such as file management ,
data transfer between file system and hardware,
memory management, scheduling of various programs
in the memory, interrupts issues.

20. ⚫The user interface is either a command line interface (CLI),
a graphical user interface (GUI), or through controls are
associated with hardware.
⚫CLI shells are text based user interfaces, which use text for
both input and output.
⚫On desktop systems, the most popular user interfaces are
the GUI shells.
⚫Most popular user interfaces are based on the X Window
System, often simply called "X".