Many of you might be confused or some people even don’t know about the truth that Linux and Macintosh both are the derivatives of UNIX OS. So here in this section I will clear the doubts about this topic.
The Unix operating system was conceived and implemented in 1969 at AT&T's Bell Laboratories in the United States by Ken Thompson, Dennis Ritchie, Douglas Mcllroy, and Joe Ossanna. It was first released in 1971 and was initially entirely written in assembly language, a common practice at the time. Later, in a key pioneering approach in 1973, Unix was re-written in the programming language C by Dennis Ritchie (with exceptions to the kernel and I/O). The availability of an operating system written in a high-level language allowed easier portability to different computer platforms. With a legal glitch forcing AT&T to license the operating system's source code, Unix quickly grew and became widely adopted by academic institutions and businesses.
But at the other side the users that are not that much familiar with the command line interface, they are not capable of operating UNIX. So to overcome this problem X-Window system is introduced and UNIX got its first web browser called Mosaic. So now the question is “What is X-Window system”.
As per Wikipedia, the X Window System (commonly X or X11) is a computer software system and network protocol that provides a graphical user interface (GUI) for networked computers. It creates a hardware abstraction layer where software is written to use a generalized set of commands, allowing for device independence and reuse of programs on any computer that implements X. X is an architecture independent system for display of graphical user interfaces which allows many people to share the processing power of a time-sharing computer; and each person uses a networked terminal that has the capability to draw the screen and accept user input. Due to the ubiquity of support for X software on UNIX, Linux and Mac OS X, it is used on personal computers even when there is no need for time-sharing. X originated at MIT in 1984. The current protocol version, X11, appeared in September 1987. The X.Org Foundation leads the X project, with the current reference implementation, X.Org Server, available as free and open source software under the MIT License and similar permissive licenses.
We see different workstations in every Linux distribution we can switch them using ctrl+F1, F2, F3 depends on how many workstation your root has given you. So basically Linux is built on UNIX and you can switch to the UNIX workstation terminal mode also in Linux. There are 7 basic terminals in Linux, first six terminals are CLI based and the 7th one is GUI, i.e. X-Window server. You can switch b/w these terminals by pressing ctrl+alt+f1, f2, f3………..f12. Depending on the version of Linux you are using.
So to switch from CLI to GUI in UNIX or MINIX OS, we have to type the command “startx” even we do it in Backtrack and BSD also because they always startup in CLI mode.