Theory - 1 :- Introduction of UNIX and LINUX.

1. Introduction to UNIX

UNIX is a powerful, multi-user, and multitasking Operating System (OS) originally developed in 1969 by a group of AT&T Bell Labs employees, including Ken Thompson and Dennis Ritchie.

Key Features of UNIX:

• Multi-user: More than one user can use the computer at the same time.
• Multitasking: The OS can run multiple programs or tasks at the same time.
• CLI (Command Line Interface): Users interact with the OS primarily by typing commands into a terminal.
• Secure & Stable: Highly reliable, which is why it is used in large servers and mainframes.

2. Introduction to LINUX

LINUX is an open-source operating system created by Linus Torvalds in 1991. It was inspired by UNIX, but it was built from scratch as a free alternative.

Key Features of LINUX:

• Open Source: The source code is free and available for anyone to view, modify, and improve.
• Highly Secure: It is very safe from viruses and malware compared to Windows.
• Lightweight: It can run smoothly even on old computers or low-hardware systems.
• Both GUI and CLI: It offers a beautiful Graphical User Interface (like Windows) as well as a powerful Command Line Interface.

3. Basic Architecture of UNIX/LINUX

Both UNIX and LINUX follow a similar layered architecture. Think of it like an onion with different layers.

The Four Core Layers:

1.    Hardware: This is the physical computer (CPU, RAM, Hard Disk, Keyboard, etc.).

2.   Kernel: The heart of the operating system. It directly interacts with the hardware, manages memory, schedules tasks, and handles file storage.

3.   Shell: The interpreter between the user and the kernel. When you type a command, the Shell reads it, translates it into machine language, and sends it to the Kernel. Common shells include bash and sh.

4.    Applications / Users: The outermost layer where users run programs like web browsers, text editors, or media players.

4. Key Differences: UNIX vs. LINUX

Feature	UNIX	LINUX
Cost	Usually expensive/commercial.	Completely free and open-source.
Developer	AT&T Bell Labs (now various companies).	Linus Torvalds (and a global community).
Usage	Mainly used in large servers, mainframes, and universities.	Used everywhere (PCs, Servers, Android Phones, Smart TVs).
Examples	macOS, Solaris, IBM AIX, HP-UX.	Ubuntu, Red Hat (RHEL), Fedora, Kali Linux.

 

5. Important Linux Directories (File Structure)

Unlike Windows, which uses drives like C: or D:, LINUX treats everything as a file, and all files start from a single root directory called / (Root).

·         /bin: Contains essential binary commands (like ls, cp, mv).

·         /home: Home directories for ordinary users (stores personal files).

·         /root: The home directory for the super user (Administrator).

·         /etc: Contains system configuration files.

·         /dev: Contains device files (like USB drives, hard disks).