Mid files are designed to product synthetic sounds using a computer's sound card. .mp3 - This extension indicates a sound file that authentically reproduces voice and/or music. Windows Media Player will open and run this kind of file. .scr - This extension indicates a screen saver file. .sit - This extension indicates a Macintosh archive StuffIt file. Take the time to investigate software tools that put you in control and allow you to block access to certain websites. If you use an online service like AOL (America Online), you can use its internal Parental Control settings to block access to various chatrooms and websites. You could even block instant messaging and email from anyone who isn't a fellow AOL user. Another benefit that open source brings to light is the speed at which its products are developed, enhanced, supported and distributed. This is because the people who regularly contribute to an open source product do so for unmotivated reasons (other than perhaps to feed the ego.) They're highly talented, they're available, and they care. 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. Since we're describing a home network that will connect to the Internet, you're strongly advised to install a protective firewall program to thwart Internet viruses, worms, or other damaging spyware code. Firewalls prevent - but they don't repair. Only anti-virus and anti-spyware programs can reverse damage. An operating system is a software program that controls how the computer's hardware (and installed software) works. It manages the activity of every component and then displays that activity as a user-friendly interface (GUI). It keeps track of where things exist on a computer's hard drive as well. But perhaps most importantly for the end-user, the operating system is responsible for translating commands issued with a keyboard and mouse into binary code (010110101 stuff) that can communicate with a set of speakers, a printer, a scanner, and more.