ScreenSavers

Screensavers were originally designed to protect computer monitors from phosphor burn-in. Early CRT monitors, particularly monochrome ones, had problems with the same image being displayed for a long time. The phosphors, used to make the pixels in the display, would glow at a constant rate for such a long period of time that they would actually discolor the glass surface of the CRT. This discoloration would then be visible as a faint image overlaying whatever else was displayed on the monitor. Advances in display technology and the advent of energy-saver monitors have virtually eliminated the need for screensavers. But we still use them.
Here are the main reasons why:

Entertainment - The most common reason we use screensavers is for the fun of it. Watching that macaroni dance across the screen to the tune of "Hey Macarena" can be a great diversion for a few minutes.

Security - By setting up a screensaver with password protection, you can walk away from your computer and feel comfortable that nobody is going to be able to see any sensitive information.

Uniform look - Many companies require all employees to use a particular screensaver. This creates a uniform and perhaps aesthetic environment and ensures that no inappropriate screensavers are displayed.

Advertisement - Companies, particularly retail businesses, that have computers in areas accessible to customers will often have a screensaver that promotes their business or product.

Information - A lot of screensavers provide either static or real-time information. A screensaver may cycle through a series of trivia questions. Another may pull stock information from a Web site and stream it across the screen.

Distributed computing - Another form of screensaver takes advantage of your computer's inactivity to process data from another source. A good example of this type of screensaver is SETI@Home, which is currently utilized by thousands of computer users. This screensaver displays a graph of the radio spectrum and processes radio-signal information received from the SETI (Search for Extraterrestrial Intelligence) servers. It sends back results based on the data processed. By using the combined processing power of all of these computers, SETI is significantly reducing the amount of time it takes to sift through all the signals received from its radio telescopes.

Here's exactly what it does:

1. To find out whether it can start the screensaver or not, Windows sends a message to the foreground application. This command is asking the application, "Can I start the screensaver?" A non-Windows program will not understand the command, and therefore will not answer it. A CBT application will understand it, but will respond with a command that means "No, I'm providing training right now." All other applications should respond positively to the command.

2. Windows then looks at the line SCRNSAVE.EXE=____ in the system.ini file to see if a screensaver has been specified. If the entry is blank, it ignores the command to execute the screensaver. But if a filename is listed, it attempts to load that file. As long as the file listed is an actual screensaver, the program executes and creates the screensaver images on top of the current desktop.

3. The screensaver continues to run until Windows detects input from the keyboard or mouse. With most screensavers, moving the mouse or pressing any key will immediately terminate the screensaver. But screensavers can be programmed to stop when only certain keys or buttons are pressed, or when the mouse is moved a certain distance. This feature is especially useful in interactive screensavers.

4. When Windows gets input that it should terminate the screensaver, it checks to see if password protection is turned on. If it is, a box pops up requiring that you enter a user name and password. Otherwise, the screensaver simply terminates.

   When password protection is active, failure to supply the correct name and password will cause Windows to continue to run the screensaver program. While this provides some security, it is important to note that Windows 95/98 screensavers create their own password dialog boxes, and request the password and user information from the system. If you are not certain of the reliability of the source of the screensaver, be careful about using password protection. Hackers can and do create screensavers that use this weak point in system security to capture passwords. This is not an issue with systems running Windows NT, which only allows screensavers to call up the system password dialog box -- they can not create their own.