What are major differences between UNIX & LINUX?

unix usually is proprietary software (with the exeption of bsd distros).
linux started as a free unix version for students (linux= linus torvalds' unix)
i do not know about unix being more stable than linux...

Most commonly known unix systems are Solaris, HP-UX and AIX
Popular linux distros are RedHat, Mandriva, Ubuntu, Fedora, Slackware, Knoppix

nowadays, both linux and unix are both text based and graphical user interface based.
most linux distros configure x-windows to start at boot, but you can choose to have it boot text based after which you can still always launch x-windows.

most popular unix system? Max OS X...

Linux and unix are fairly similar, not a lot of difference between the two. I could go into alot of detail about both but I'm tired and can't brain right now lol. Just to clarify though, linux isn't a GUI operating system. There are Many GUIs available for linux, usually provided through the X Windowing System. Probably the two most popular at this time are KDE and GNOME. Pretty much all GUIs supported by linux run under nearly all Unix like operating systems.

Unix itself, isn't so much an operating system these days as a set of criteria for an operating system. In 70s, the original operating system called Unix was developed by Bell Laboratories (At&t Unix). It turned out to be extremely popular, and the first Unix variant, was developed by Berkley University. This operating system was called BSD Unix, an acronym for Berkley Software Distribution. Over time many Unix operating systems came to be, some based on BSD, some based on AT&T Unix. Most modern*nix operating systems have roots from either one.

These days with so many Unix type operating systems there is what is called Unix certification. If the operation meets a long criteria of requirements, then (after the software company pays a fair bit of money), it can be certified as Unix. Mac OS X, is certified Unix, as well as a large number of others. Operating systems that are Unix like, but do not meet the criteria to be certified as Unix, can be collectively referred to as*nix operating systems.

Linux, is a*nix operating system. The Linux kernel came to be in the early 90s, when Linus Torvaldis decided to develop his own version of Minix. It rapidly grew in popularity, and has attracted a large community of developers. There are so many Different operating systems built on Linux these days that it's not funny. They are usually referred to as Linux Distributions. Selecting the right Linux distribution for your needs can be a daunting task. Probably at the moment the most popular distro is Ubuntu, due to it's easy installation procedure and simple to use interface.

I hope that has sort of helped to answer your question on the difference betwen the two. To answer your second question, is kind of hard. In the industry there are alot of applications for*nix operating systems, it makes it hard to tell exactly. In the small server market, Linux is probably the most popular. For webservers the most common configuration is a LAMP (Linux, Apache, Mysql and PHP) server. It also has some presence in the desktop market, albeit nowhere near as much as Windows. But in the mainframe and larger server market different variants of Unix would tend to be more popular. Different manufacturers of server hardware tend to have their own Versions of Unix (such as HP/UX etc).

You shouldn't take all of what I have said as 100 percent true and accurate, but I think I got it fairly right. It just gives you a basic idea on the subject. If you want to read more, Wikipedia has some good articles on many different Unix and Linux variants.:)

I think linux is more user-friendly to common users.Some of linux distros are turnning very easy to use such as ubuntu and open suse.However,unix is mainly still a more specialized OS mainly popular among IT workers because they are so stable and some of them are not open-sourced.

Unix was built by Dennis M. Ritchie from a scratch. Dennis M. Ritchie is also known for his great contribution to computer science - The C language. Later Unix was sold.
A man called Andrew S. Tanenbaum built an operating system inspired by the Unix for educational purposes. He named it Minix for "Minimal Unix". Now what Linux did was that he built the support for X windows (GUI) and renamed it as LINUX.
Today there are thousands of contributor for the LINUX.
So you see Linux can't be a less stable than Unix.
No doubt Linux is more popular.

Generally speaking Linux is just a kernel. many other applications added to it then it becomes a distribution. like Redhat, Mandrake etc.

As far as Unix is concerned Unix is complete Operating system.
Mostly all unix available out there are proprietary with exception of BSD unix which is Open Source.

In big companies mostly they prefer Unix as its been there for a very long time and has already proved its metal.
But again there are exceptions eg. companies like Google uses Linux at its base.

I hope this has cleared your doubt.

Take care.