The document provides an introduction and history of UNIX. It describes how UNIX originated from MULTICS in 1969 and was ported to new hardware in 1971. To improve portability, Ken Thompson created a new programming language called B and rewrote UNIX in this language. Dennis Ritchie later modified it to use the C programming language. The document also outlines some key features of UNIX including being multi-user, multitasking, portable, secure, and able to communicate through networking. It describes the organization of UNIX with utilities, applications, the shell interface, and the kernel which manages resources and program execution.

1. UNIX
AN INTRODUCTION
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2. • In 1965 Bell Laboratories ,general Electrical company and
Massachusetts Institute of Technology developed an
operating system called MULTICS.
• MULTICS was named as UNIX in1969.
• In 1971 Unix was ported to PDP-11 computers.
• But this version was not portable for new machines.
• To resolve this problem Ken Thompson created a new high
level language called “B” and rewritten the whole UNIX
code in this high level language.
• Dennis Ritchie modified it to a new high level language
called “C”.
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HISTORY

3. Features of UNIX
Multi-user OS:
• Multi –user means more than one user.
• Terminals have monitors and keyboards that are connected to
main computer .
• A user is allowed to sit on different terminals and access the
main computer and its resources by giving his login name
and password.
• These terminals that are connected to the main computer are
called Dump terminals.
• They can never act as independent machines and are fully
dependent on main computer.
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4. • Multitasking
Capacity of an OS to perform multiple task
simultaneously.
It uses Time sharing techniques.
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5. • Portability
Ability to adapt to different computers
• Security
To prevent unauthorized access.
Password to individual user:
The system will log on for a particular user
after verifying his user name and password.
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6. File access security:
At file level there are Read ,Write and eXcute
permissions for each file .
File Encryption and decryption:
Unreadable format
Communication:
Exchange data through network among its users.
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7. Unix System Organisation
• Utilities and Applications:
Represents user programs and commands.
• Shell
Command interpreter
Interprets the user commands and conveys
them to the kernel that executes them.
Mediator between user and kernel.
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8. • Types of shells
Commonly used shells are
1)Bourne shell :
Default shell.
The prompt of this shell is dollar ($).
2)C shell:
The prompt of this shell is %.
3)Korn shell:
The prompt of this shell is dollar ($).
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9. • Kernel
 Heart of the Unix System.
 Loaded into the memory whenever the system is
booted.
 It manages resources such a files, memory, I/O etc
and also keeps track on program execution.
 It doesnot interact with the user directly .
 Shell is used as a mediator b/w user and kernel.
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10. THANK YOU
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