Datasheet

If you’re about to upgrade to Leopard from an earlier version of Mac OS X, I
feel obliged to mention a major pitfall to avoid: One very specific misplaced
click, done while installing your new OS, could erase every file on your hard
drive. The appendix describes this situation in full and loving detail, and it
contains other important information about installing Leopard that can make
upgrading a more pleasant experience.
Gnawing to the Core of OS X
The operating system (that is, the OS in Mac OS X) 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 Mac OS X and your Mac, the oper-
ating system
 Manages memory
 Controls how windows, icons, and menus work
 Keeps track of files
 Manages networking
 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 that
software works its 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)
So, armed with a little background in operating systems, take a gander at the
next section before you do anything else with your Mac.
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Part I: Introducing Mac OS X Leopard: The Basics
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