What Does the Mountain Lion Operating System Do?
The operating system (that is, the OS in Mac OS X Mountain Lion) is what makes a Mac a Mac. Without it, your Mac is a pile of silicon and circuits — no smarter than a toaster.
So what does an operating system do? you ask. Good question. The short answer is that an operating system controls the basic and most important functions of your computer. In the case of OS X and your Mac, the operating system
Controls how windows, icons, and menus work
Keeps track of files
Does housekeeping (No kidding!)
Other forms of software, such as word processors and web browsers, rely on the operating system to create and maintain the environment in which they work their magic. When you create a memo, for example, the word processor provides the tools for you to type and format the information. In the background, the operating system is the muscle for the word processor, performing crucial functions such as the following:
Providing the mechanism for drawing and moving the on-screen window in which you write the memo
Keeping track of a file when you save it
Helping the word processor create drop-down menus and dialogs for you to interact with
Communicating with other programs
And much, much more (stuff that only geeks could care about)