The document provides information on the history and features of the UNIX operating system. It discusses that UNIX was first created in 1969 at Bell Labs and made commercially available in 1977. It then describes several key features of UNIX including being multi-tasking, multi-user, having a hierarchical file system, shell interface, and being portable across different hardware. The document also discusses the UNIX kernel and system architecture, including the kernel interacting with hardware and managing tasks like memory, files, and processes. It provides information on different UNIX shells like the Bourne shell, C shell, and Korn shell.

2. History
UNIX
1
 The first version of UNIX was created in 1969
by Kenneth Thompson and Dennis
Ritchie, system engineers at AT&T's Bell Labs.
It went through many revisions and gained in
popularity until 1977, when it was first made
commercially available by Interactive Systems
Corporation.
 UNIX, multiuser computer operating
system. UNIX is widely used for Internet
servers, workstations, and mainframe
computers

3. 2
UNIX
 Multi-Tasking : Unix is a powerful multi-tasking operating system; it means when a active task in in process, there can be a simultaneous
background process working too. Unix handles these active and background threads efficiently and manages the system resources in a fair-
share manner.
 Multi-User Operations: UNIX is a multi-user system designed to support a group of users simultaneously. The system allows for the
sharing of processing power and peripheral resources, white at the same time providing excellent security features.
 Hierarchical File System: UNIX uses a hierarchal file structure to store information. This structure has the maximum flexibility in
grouping information in a way that reflects its natural state. It allows for easy maintenance and efficient implementation.
 UNIX shell: UNIX has a simple user interface called the shell that has the power to provide the services that the user wants. It protects the
user from having to know the intricate hardware details.
 Pipes and Filters: UNIX has facilities called Pipes and Filters which permit the user to create complex programs from simple programs.
 Utilities: UNIX has over 200 utility programs for various functions. New utilities can be built effortlessly by combining existing utilities.
 Portability: The system is written in high-level language making it easier to read, understand, change and, therefore move to other
machines. The code can be changed and complied on a new machine. Customers can then choose from a wide variety of hardware vendors
without being locked in with a particular vendor.
 Machine-independence: The System hides the machine architecture from the user, making it easier to write applications that can run on
micros, mins and mainframes.
Salient Features

4. Features of Unix
▸ Open Source: Linux code is freely available to
all and is a community based development
project.
▸ Tools/Utilities/add-ons
▸ Security: It provides security in three ways
namely authenticating (by assigning password
and login ID), authorization (by assigning
permission to read, write and execute) and
encryption (converts file into an unreadable
4

5. 5
Why Use Linux
Linux is completely different from other operating systems in many ways.
•It is an open source OS which gives a great advantage to the programmers
as they can design their own custom operating systems.
•It gives you a lot of option of programs having some different features so
you can choose according to your need.
•A global development community look at different ways to enhance its
security, hence it is highly secured and robust so you don't need an anti virus
to scan it regularly. Companies like Google, Amazon and Facebook use linux
in order to protect their servers as it is highly reliable and stable.
•Above all you don't have to pay for software and server licensing to install
Linux, its absolutely free and you can install it on as many computers as you
want.
•Its completely trouble free operating system and don't have an issue with
viruses, malware and slowing down your computer.

6. 3
UNIX
UNIX System Architecture

7. 4
UNIX
UNIX System Architecture
The main concept that unites all the versions of Unix is the following four basics –
 Kernel : 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.
 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. 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.
 Commands and Utilities : 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.

8. 5
UNIX
UNIX Kernel System
The Kernel is the heart of the
UNIX, which interacts with the
actual hardware in machine
language. The Kernel has various
functions it manages files, carries
out all the data transfer between
the file system and the hardware,
and also manages memory.

9. 6
UNIX
UNIX Kernel System
• Assembly language programs may invoke system calls directly without a system call library,
however. Programs frequently use other libraries such as the standard I/O library to provide a
more sophisticated use of the system calls. The libraries are linked with the programs at
compile time.
• The figure partitions the set of system calls into those that interact with the file subsystem and
those that interact with the process control subsystem. The file subsystem manages files,
allocating file space, administering free space, controlling access to files, and retrieving data
for users.
• Processes interact with the file subsystem via a specific set of system calls, such as open (to
open a file for reading or writing), close, read, write, stat (query the attributes of a file).
• The file subsystem accesses file data using a buffering mechanism that regulates data flow
between the kernel and secondary storage devices.
• Device drivers are the kernel modules that control the operation of peripheral devices. Block
I/O devices are random access storage devices alternatively, their device drivers make them
appear to be random access storage devices to the rest of the system.
• The process control subsystem is responsible for process synchronization, inter process
communication, memory management, and process scheduling.
• The memory management module controls the allocation of memory.
• The scheduler module allocates the CPU to processes. It schedules them to run in turn until
they voluntarily relinquish the CPU while awaiting a resource or until the kernel preempts

10. 7
UNIX
Types Of Shell
 The Bourne shell (sh) is a shell, or command-line interpreter, for computer
operating systems. The Bourne shell was the default shell for Version 7 Unix.
Developed by Stephen Bourne at Bell Labs, it was a replacement for the
Thompson shell, whose executable file had the same name — sh.
 The C shell (csh) is a command shell for Unix-like systems that was originally
created as part of the Berkeley Software Distribution (BSD) in 1978. Csh can be
used for entering commands interactively or in shell scripts. The shell introduced a
number of improvements over the earlier Bourne shell designed for interactive
use. These include history, editing operations, a directory stack, job control and
tilde completion.
 The Korn shell is the UNIX shell (command execution program, often called
a command interpreter ) that was developed by David Korn of Bell Labs as a
comprehensive combined version of other major UNIX shells. Incorporating all
the features of C shell ( csh ) and Bourne shell , the Korn shell is considered the