Device independent components work right no matter what model of device you use them with. For example, if the graphic file format in your publication is device independent, the results you see on paper will look about the same whether you print to an HP DeskJet, an Apple LaserWriter, or a high-resolution Linotronic image setter (the graphic will be printed at whatever resolution the printer uses).
Device dependent components by contrast, work right only with a particular model of the device. A device dependent bitmap graphic looks the way it's supposed to only on a particular type of monitor-on other screens it looks funny or may not display at all.
All the programs that run under Windows and the Macintosh are device independent. A given program doesn't have to worry about how to work with every mouse, keyboard, printer, screen, or scanner on the market. Instead, as long as the environment has a software control module (or driver) for the devices in your system, every program will automatically produce the expected results. Of course, there may be some variations due to the differing capabilities of different models. For instance, text you print on a 300-dot-per-inch laser printer will not be as smooth as text from a 2540-dot-per-inch image setter. But the basic look of the text will still be the same if you have a device independent system.