linux
Windows 8 is the most current windows client operating system.
Windows Vista is the operating system.
If the PC is made by Apple then the current Apple operating system is 100% compatible. Other PCs with other operating systems will have varying degrees of compatibility with the current Apple operating system.
Every operating system is unique to the person who is using it!
A user communicates with the operating system by using a keyboard. You can also communicate with the operating system by using a mouse.
compitibility
Apple's Macintosh computers use Apple's operating system known as OSX. The current version is OSX 10.8.#. Macintosh computers can also run the Windows and Linux operating systems, but those systems are not included in the purchase of the computer.
operating system
Linux
there is no "linux operating system". linux is merely a kernel that operating systems can be built upon, of which there are dozens if not hundreds
An operating system is a necessary concept of using a modern computer. It is not a matter of "popularity."
The operating system communicates to the computer hardware using the GUI program.