At the very end of this process, the computer looks for an operating system and if not found, it will prompt the user to tell it where it is. Earlier computers didn't have an operating system and if you have experience with the computers of the early eighties, you'll remember that most to them didn't even have a hard drive! It hasn't gone anywhere, but its competition with commercial software is fierce - so fierce that it tends to fall on the back burner among new computer users. This is unfortunate because shareware has so many advantages over commercial software. One of those advantages is its cost. On the whole, shareware is generally cheaper than commercial software. There are many creative uses for home networking, however it's an ideal situation when upgrading each computer to the same capability is financially out of the question. On a home network, each computer has access to the equipment of the better machine in the group as if that equipment were their own. scr - This extension indicates a screen saver file. .sit - This extension indicates a Macintosh archive StuffIt file. They will not open on a Windows system without a special utility. .ttf - This extension indicates a font especially designed for use on a Windows system. It stands for "True Type Font. Hold the can perfectly vertical and spray the fan being careful not to spray the dust off the fan onto other sensitive parts of the computer like circuit boards or inside the motor casing. Wipe up remaining dust with your anti-static rag and then reassemble the computer. One thing that you certainly don't want to use to remove computer dust is a vacuum cleaner. A disk drive that's clogged with unnecessary and unused files is disk drive that works harder than it has to. Although Window's defrag system can ease some of the stress that these files place onto the drive, it doesn't do much to get rid of the problem in the first place. This is because the defrag program simply organizes the files in a system that makes it easier for the computer to access.