UNIX is a computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs.
Today's UNIX systems are split into various branches, developed over time by various commercial vendors and non-profit organizations.
At a first glance: UNIX similarity with ...
Visually (not functionally, though!), Unix is similar to DOS. UNIX file system when viewed in the command prompt looks like a hierarchical tree, similar to DOS. In UNIX however, everything is a "file". Real files, directories, device drivers, and so on.
Directories are special files that hold the names of other files or other directories. Note that directories are separated by a forward slash ( / ) not a backslash ( \ ) like in DOS.
UNIX is however much more advanced in terms of security. Permissions apply to directories as well as files.
UNIX on personal computers (desktops)
Since the 1980's Unix's main competitor Windows has gained popularity due to the increasing power of micro-computers with Intel-compatible processors. At that time, Windows had better graphical user interface and more tools for home use and was also more user friendly.
In recent years, however, a new version of Unix called Linux, also specifically developed for micro-computers, has emerged. It can be obtained for free and is therefore a lucrative choice for individuals and businesses.
Linux provides a graphical user interface (GUI), so to a general home user, it no longer has the look of a black DOS-like screen, but it provides an environment very similar to the Windows one.
Advantages of UNIX over other OSs
Stability: Even though Microsoft made many advancements in their software, UNIX is more stable and does not crash as often as Windows operating system; therefore, it requires less administration and maintenance.
Flexibility: UNIX is flexible and can be installed on many different types of machines, including main-frame computers, supercomputers, and micro-computers.
Performance: UNIX possesses much greater processing power than Windows, especially due to its ability to address large address spaces. For this reason, UNIX is the operating system of choice for web servers.
Security: Although especially server versions of Windows combined with domain and file sharing security suffice most daily uses, general user or home versions of Windows lack necessary security. UNIX has greater built-in security and permissions features than Windows.Open source: Because UNIX is an open-source operating system, anyone interested in implementing it can research bugs and holes that affect the use. With the flexibility and control, UNIX is attractive to developers.
Lower cost: Software upgrades from Microsoft often require the user to purchase new or more hardware or prerequisite software. How many of us did buy a new and more powerful computer only because the new operating system would not run on our old computer? That is not the case with Unix. Linux and BSD operating systems are mostly free and open-source operating systems.
You mentioned DOS, do you have any details about that?
Yes, a page on MS-DOS is here.