But without seeing the extension, you wouldn't know it unless you double-clicked on it. The following list defines some of the most common extensions that you'll find on your computer. .au - This extension indicates a sound file. Most sound players will load up and play this kind of file. .art - This extension indicates an image file that was compressed with AOL (America Online) technology. Nicotine and tar mean certain death when it comes to computer fans, however should you find a need to clean the fan, do so with extreme care. It's quite easy to cause more damage from cleaning so if you're not comfortable with cleaning your PC yourself, take it to a shop for servicing. Otherwise, you can unplug and disassemble the computer to do it yourself. For example, when you're faced with an electronic system, look for a main menu. Most main menus display themselves as soon as a device is turned on, so chances are that if you're standing before a device that shows a bunch of choices to do something, you're looking at a main menu. The buttons on these main menus of course take you to additional menus, which in turn give you even more choices to make. An uninstall program can remove only the files it placed onto a hard drive during its install routine. So while Windows' Add/Remove Programs can remove an entire program, you'll need to get rid of those pesky little things with a more advance file cleaner like CleanSweep for example. CleanSweep is a unique program that will specifically seek out files that are no longer associated with a program, and then ask if you want to delete them. If you can remember that there are hoards of alternatives to costly commercial software (and you make the effort to get it), you'll discover that you can keep up with the rest of the computer industry at a significantly cheaper cost than if you attempted to pay your way down the software aisle. Software piracy just isn't the answer. If you're familiar with MS-DOS at all, you'll recall that it's a command-driven operating system that performs functions issued at the C:> prompt. The only way to get an MS-DOS computer to do something was to type a command at this prompt and if you can imagine, it was a rather cumbersome way to use a computer.