What is the difference/comparison between Unix and Linux ?

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 numorous differences. 

Well to be specific Linux is considered as Unix-Like Operating system coming under the category of UNIX clones. A clone is a program (i.e., an operating system or an application program) that has functions and behavior similar to another program but which does not contain source code from that program.

UNIX was developed and evolved more as a licensed version or proprietary software.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.

Even now most UNIX operating system are proprietary as they are mostly commercially used like Oracle's Solaris, Hewlett-Packard's HP-UX, and IBM's AIX. Well there are also some open source OS for UNIX like Open Solaris, OpenBSD.

Coming to Linux kernel you can find a long list of free and opensource operating system like CentOS, Scientific Linux, Fedora, OpenSUSE, Ubuntu etc. For commercial version there is Red hat Linux, SUSE etc.

Linux can be much more flexible as compared to Unix as they can be installed on almost any hardware(NOT ALL). But Unix OS are very restricted when it comes for the supported hardware for example HP-UX is available on PA-RISC and Itanium machines. Solaris is available on SPARC and x86. AIX is only for power processors etc.

Kernel can be considered the HEART of any operating system. Now as explained in the history part Linux is just an kernel and integrating it with other features like libraries, editors, compilers makes it an Operating System. 

The source code for most UNIX kernel specially commercial versions are not available freely. On the other hand most Linux OS source code are free available under the GPL and can be read, modified and used by any and everyone.

Linux being open source their patches are released in the form of source code which can be manually and updated. Now one negative point on this one can be that these patches are not much tested for bug as compared to commercial version of UNIX. In case of Linux based on the feedback of users and developers the bugs are fixed and patches are released. But in case of UNIX developers test the patch multiple times before releasing it to the update server of their OS.

NOTE: In case of commercial version of Linux the patches are checked and verifed prior releasing it to their relative OS. Re-revised version of OS are released at regular intervals with all the bug fixes as developed.

UNIX OS seems to be more stable in terms of releasing patches or upgrades and the code works for longer time for the same driver as compared to Linux.

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.

Well mostly Linux/Unix are preferred to be used on CLI rather than GUI in corporate world. But still to make things easier both the OS offer different type of GUI tools for administrators.

In Red Hat - system-config-*

In HP-UX - SAM (System Administration Manager)

In SUSE - YaST

As per the command perspective, there can be seen many differences 

For example to install a package

In Red Hat - rpm -i file

In Solaris - pkgadd -d pkgfile

IN HP-UX - swinstall -s depot software

IN AIX- installp - [-c] FileSet

Location of the system init scripts is different on both the types of OS

System	Location
HP-UX	/sbin/init.d
AIX	/etc/rc.d/init.d
Irix	/etc/init.d
Solaris	/etc/init.d
Red Hat	/etc/rc.d/init.d
SUSE	/etc/rc.d/init.d
Debian	/etc/init.d
Slackware	/etc/rc.d

As discussed in earlier part of this article most UNIX use their own hardware for their OS their cost price rises accordingly where on the opposite side getting a commercial version of Linux OS is very much cheaper.

What is a Kernel in Linux?
What is swappiness and how do we change its value?
What is GRUB Boot Loader ?