Datasheet

Although there are places where this old convention still exists, Mac OS X mostly uses Unix’s method
of describing file paths: a series of directories from the root directory all separated by slashes, as in
/Applications/Utilities/Terminal.app. The root directory contains all the files and directories on
a Mac OS X system and is referred to simply as
/. The path /Applications refers to a file or directory
named
Applications in the root directory. A path that begins with the root slash is called an absolute (or
full) path because it describes a precise file location. If the root slash is not included, the path is called a
relative path because it is relative to your current location.
If you look in
/Applications/Utilities in the Finder, you might notice that there is no
Terminal.app; instead there’s just a program called Terminal. By default, Finder and other applica-
tions hide file extensions such as
.app and .txt from you. So the application at /Applications/
Utilities/Terminal.app
appears simply as Terminal. The Core OS makes no attempt to hide
extensions from you; if you browse the file system using Mac OS X’s command-line interface, you can
see all these extensions. You learn more about Mac OS X’s command-line interface later in this chapter.
Darwin is composed of several parts, including a kernel, a system library, and numerous commands, as
illustrated in Figure 1-3.
Figure 1-3
Applications
Frameworks and UI
Graphics and Media
Core Operating System
Command-
line Tools
System Library
Kernel
7
The Mac OS X Environment
Program, Process, Application — What’s the Difference?
Much of the time you can use the terms program and process interchangeably to refer to
something that’s executable. But these terms do have distinct definitions. The word pro-
gram refers to a file on disk containing a series of computer instructions. When this file
is executed (or run, launched, and so on) the computer starts processing the instruc-
tions in the file. Process describes the act of executing the file. To borrow an example
from the kitchen, it may help to think of a program as a recipe for baking a cake, and
process as the act of baking that cake.
Ultimately, an application is just a program. On Mac OS X, however, programs can take
many forms: simple tools typed in a command-line interface, a program you can double-
click in the Finder, a plug-in file loaded by other programs, and so on. To avoid some
confusion, we use the term application in this book to refer specifically to those programs
that appear in the Finder; we use the term program when no distinction is necessary.
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