The difference between screensavers and wallpaper is that wallpaper is a static image that acts as a background image for the computer desktop, whereas the screensaver is a computer program that places a moving image on the computer screen while it is not in use. The screensaver hides the computer desktop, both to prevent damage to the monitor and for security purposes. Sometimes, the screensaver on a computer will activate other computer programs that can run in the background, such as an antivirus or anti-spyware scan. Both wallpaper and screensavers are commonly used on both personal and business computers.
Screensavers at one time served a more functional purpose than they do now. Older computer monitors used cathode-ray tube (CRT) technology, similar to old television sets. If a static image was left on the screen on these CRT monitors, or plasma monitors as well, the image could potentially "burn" onto the screen and cause damage. The moving images of the screensaver prevented this image burn from occurring on the screen. This is no longer a concern on LCD monitors, but many people still use screensavers for aesthetics and privacy, as well as to allow antivirus programs to scan the computer while it is not in use.
It is possible to set the screensaver program to require a password when someone tries to take the screensaver off and resume looking at the desktop. This is very helpful in office environments if one frequently walks away from the computer; setting the screensaver password is a quick, basic level of security to prevent others from logging on to the computer. Aside from these functional purposes, both screensavers and wallpaper serve decorative purposes as well. There are many different screensavers and wallpaper options pre-loaded onto most computers, or one can create a new one using favorite family photos, for example.
While screensavers serve a practical purpose on the computer, wallpaper is just for decoration. Wallpaper, or a background desktop image, simply fills up the desktop on which the program icons are located. It is possible to make the desktop image anything that one wants it to be; many people use favorite photos, or there are a nearly endless desktop wallpaper options that can be found for free online. Desktop wallpaper can be changed as often as one wants. Both screensavers and wallpaper are great, free, and easy ways to personalize one's computer and to increase its security.