Difference between Linux and UNIX

Infact Linux & UNIX are very similar. Both share many common applications such as a. Office applications (Example: OpenOffice.org) b. Development tools (Example: PHP, Perl, Python, GNU c/c++ compilers) c. Shells (Example: ksh, csh, bash) d. GUI, File and Windows Manager (Example: KDE, Gnome) and much more.

However we will engage soon to find out the distinction in order to acquire a sharp idea over them. 

1. Explanation
1. UNIX: UNIX is a certification for operating systems. It is a very old operating system and was intended to operate on large computers and mainframes.
2. Linux:  Linux is based on UNIX and it is an operating system kernel. Linux has never been certified as being a version of UNIX, so it is described as being "Unix-like."
2. Development
1. UNIX: The UNIX standard evolved from the original UNIX system developed at Bell Labs (Universities & Research Organization). UNIX Operating System names are:

                                                              i.      AIX – Developed thru IBM.

                                                           ii.      Solairs – Sun Solaris.

                                                         iii.      OS X – Mac

                                                          iv.      HP-UX (from Hewlett-Packard)

                                                            v.      IRIX (from Silicon Graphics)

2. Linux: Linux, which is developed by Linus Torvalds (a university student), is based on the UNIX system but does away with the complex mechanisms that make learning UNIX very steep. Linux distribution (Operating System) names are:

                                                              i.      Redhat Enterprise Linux

                                                           ii.      Fedora Linux

                                                         iii.      Debian Linux

                                                          iv.      Suse Enterprise Linux

                                                            v.      Ubuntu Linux

3. Cost & Ownership
1. UNIX: UNIX is proprietary software and it is required to buy in order to use it.
2. Linux:  Linux, on the other hand is a free OS licensed under the GNU GPL & developed by the Community. 
4. User Friendly  
1. UNIX: UNIX does not support Tab key; UNIX is CUI i.e. Character User Interface.
2. Linux: Linux is considered as most user friendly UNIX like operating systems. It makes it easy to install sound card, flash players, and other desktop goodies.  Linux support Tab key; while Linux is GUI graphical user interface.
5. Platform i.e. Hardware Compatibility
1. UNIX: Platform dependent; all of the releases for UNIX are built with the latest high end hardware in mind and it is not usable in the common desktop computer.
2. Linux: Platform independent; Linux, on the other hand, can scale reliably across different hardware platforms making it a good choice for most people.
6. File System
1. UNIX: jfs, gpfs (AIX), jfs, gpfs (HP-UX), jfs, gpfs (Solaris).
2. Linux: ext3 or ext4 file systems.
7. Security i.e. Firewall
1. UNIX: UNIX operating systems use its own firewall product (Example: Solaris UNIX comes with ipfilter based firewall) or required to purchase 3rd party firewall such as Checkpoint UNIX.
2.  Linux:  Linux use open source netfilter/iptables based firewall tool to protect the server and desktop from the crackers and hackers.
8. System Administration Tools
1. UNIX: UNIX uses its own tools such as SAM on HP-UX. 
2. Linux: Suse Linux use Yast; Redhat Linux use GUI tools called redhat-config-*.