There are not much differences between Linux and UNIX in terms of most of the commands and working if looking from an end-user perspective. But internally in the sense of hardware, kernel, patches etc there are so many differences. Linux is considered as Unix-Like Operating system coming under the category of UNIX clones.
#UNIX was developed and evolved more as a licensed version. It was used more for commercial purpose. This was one of the reason for Linux to be developed as a free operating system by Linus Torvalds. Once the Linux kernel was developed later it was released under GPL (GNU General Public License) integrated with libraries, compilers, text editors transforming it into an operating system and releasing worldwide as opensource.
#Linux can be much more flexible as compared to Unix as they can be installed on almost any hardware. But Unix OS are very restricted when it comes for the supported hardware.
#Linux has very high scalibility be it in terms of hardware architectures or filesystem as it suports many of them unlike UNIX OS which supports very few type of filesystem.
#UNIX Operating System Names
A few popular names:
HP-UX
IBM AIX
Sun Solairs
Mac OS X
IRIX
#Linux Distribution (Operating System) Names
A few popular names:
Redhat Enterprise Linux
Fedora Linux
Debian Linux
Suse Enterprise Linux
Ubuntu Linux
#Common Things Between Linux & UNIX
Both share many common applications such as:
GUI, file, and windows managers (KDE, Gnome)
Shells (ksh, csh, bash)
Various office applications such as Apache OpenOffice
Development tools (perl, php, python, GNU c/c++ compilers)
Posix interface