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An on-screen display (abbreviated OSD) is an image superimposed on a screen picture, commonly used by modern televisions, VCRs, and DVD players to display information such as volume, channel, and time. more...

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In the past, most adjustments on TVs were performed by means of analog controls, like potentiometers and switches. This is still used in modern monochrome portable TVs. After remote controls were invented, digital adjustments became common. They needed an external display, which was LED, LCD, or VFD based. Including this display increased manufacturing costs.

When electronics became more advanced, it became clear that adding some extra devices for an OSD was cheaper than adding a second display device. TV screens had also become much bigger and could display much more information than a tiny second display. OSDs display graphical information superimposed over the picture, which is done by synchronizing the reading from OSD video memory with the TV signal.

On-screen displays first began to appear in the 1980s on televisions. By the mid-1990s, VCRs with these displays became widely available. This made it possible to reduce the size (and cost) of the VFDs used in VCRs. All DVD players also use on-screen displays. Many PAL television sets use the internal Teletext decoder's graphics rendering system to further reduce costs.

Some computer software also uses OSDs, especially support programs for so-called "enhanced keyboards", which often had additional media keys for actions like skipping through music tracks and volume adjustment. Their use outside this field, however, is still uncommon. On-screen displays are also used in camcorders, and can display various information both on the viewfinder and on the TV set the camcorder is connected to.

The complexity of graphics offered by such displays has greatly increased over the years, from simple monochrome images to intricate graphical user interfaces.

A common problem with the use of an on-screen display is diagnostics in case a television's display system is damaged. Without any external screens, it is almost impossible (without opening the television) to determine the source of the error. Television accessories that depend heavily on OSDs, such as VCRs or DVD players, are also very difficult to configure without the use of a television. On older VCRs, for example, it was possible to set up recording timers without turning on the TV; a modern VCR requires the user to turn on his or her TV to do so. However, the drawbacks of using OSDs are few in comparison to its benefits, which has led to its widespread use.

Read more at Wikipedia.org