The data that a program receives is called input and data that the program generates is called output. Other times, the data is unknown. If the program were working with a simple algebra equation like, "x + 5 = y," the variables "x" and "y" would be unknown pieces of data. Then let's say that the user of that computer downloads and installs Program B. Program B uses a file that Program A installed much earlier, but when Program B is run, errors popup. Those errors are the result of Program B attempting to use an outdated (shared) file that was installed by Program A. In order to fix that problem, the user would have to download an updated version of the shared file (which to say the least - is not an easy thing to find or do). As an example, to load up Microsoft's simple editing program, you had to type the name of the drive that the program was on, the directory that the program was in, and then the name of the program. So if Microsoft Edit was in a directory or folder named "Process," you could start the program by typing, "C:>process\edit. Basic GUI Terminology Knowing What You're Working With Helps Technicians Getting help with your computer software can be easier when you know the correct terms to use. One of the biggest problems that new computer users have with technical support is not knowing how to correctly describe the problem that they're having. It's costly to produce and as you can probably guess, that cost is passed on to the end user: the consumer. Open source software on the other hand is free. Free to download, free to install, free to use, free to modify, and free to share. Started over twenty years ago, it's a phenomenon that is gaining in both popularity and exposure. " In short, the fan is responsible for keeping a computer's motor cool and this motor is what keeps the computer's hard drive and peripherals functioning the way you need them to, which translates to "fast." A dirty fan doesn't rotate fast enough to keep that motor cool and a completely clogged fan just stops rotating altogether.