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A screensaver (or screen saver) is software that controls a Computer monitor of the host computer with the intent of preventing screen burn-in for a screen susceptible to it. Generally, a screensaver starts controlling a monitor when the computer has been idle for a designated period of time and fills the screen either with black (all pixels off) or with changing graphics that tend to prevent each pixel from being on for a long time. Although monitors were commonly constructed with screen technology that was susceptible to burn-in (CRT and plasma display), most modern monitors are LCD which are not. Notably, another modern technology, OLED, is susceptible.
In addition to the feature described by its name (saving a screen), a screensaver may provide other features. It may provide physical security by requiring a password to exit the screen control mode. Some use otherwise-idle computer resources to do useful work, such as processing for volunteer computing projects.
Many modern devices such as televisions and other digital entertainment devices include a screensaver.
Using a screensaver with a flat panel or TFT LCD screen not powering down the screen can actually decrease the lifetime of the display, since the fluorescent backlight remains lit and ages faster than it would if the screen is turned off and on frequently. As fluorescent tubes age they grow progressively dimmer, and they can be expensive or difficult to replace. A typical LCD screen loses about 50% of its brightness during a normal product lifetime. In most cases, the tube is an integral part of the LCD and the entire assembly needs to be replaced. This is not true of LED backlit displays.
Thus the term "screen saver" is now something of a misnomer – the best way to save the screen and also save electricity consumed by screen would simply be to have the computer turn off the monitor. Screensavers displaying complex 3D graphics might even add to overall power draw.
For CRTs used in public, such as an automated teller machine (ATM) and railway ticketing machine, the risk of burn-in is especially high because a stand-by display is shown whenever the machine is not in use. Older machines designed without burn-in problems taken into consideration often display evidence of screen damage, with images or text such as "Please insert your card" (in the case of ATMs) visible even when the display changes while the machine is in use. Blanking the screen is not a valid option as the machine can be perceived as out of service. In these applications, burn-in can be prevented by shifting the position of the display contents every few seconds, or by having a number of different images that are changed regularly.
Later CRTs were much less susceptible to burn-in due to improvements in phosphor coatings, and because modern computer images are generally lower contrast than the stark green-on-black or white-on-black text and graphics of earlier systems. LCD computer monitors, including the display panels used in laptop computers, are not susceptible to burn-in because the image is not directly produced by phosphors although they can suffer from a less extreme and usually non-permanent form of image persistence.
While modern screens are not susceptible to burn-in, screensavers are still used for other purposes. They usually feature moving graphics and sometimes sound.
At least one screensaver, Johnny Castaway, told a humorous animated story over many months. The ability of screensavers to divert and entertain is used for promotion, especially to build Marketing buzz for "event-based" products such as film.
The screensaver is also a creative outlet for computer programmers. The Unix-based screensaver XScreenSaver collects the display effects of other Unix screensavers, which are termed "display hacks" in the Jargon File tradition of US computer science academics. It also collects forms of computer graphics effects called , such as were originally produced by the demoscene.
The first screensaver was allegedly written for the original IBM PC by John Socha, best known for creating Norton Commander; he also coined the term screen saver. The screensaver, named scrnsave, was published in the December 1983 issue of the Softalk magazine. It simply blanked the screen after three minutes of inactivity.
By 1983 a Zenith Data Systems executive included "screen-saver" among the new Z-29 computer terminal's features, telling InfoWorld that it "blanks out the display after 15 minutes of nonactivity, preventing burned-in character displays." The first screensaver that allowed users to change the activating time was released on Apple Computer's Apple Lisa, in 1983.
The Atari 400 and 800's screens would also go through random screensaver-like color changes if they were left inactive for about 8 minutes. Normal users had no control over this, though programs did. These computers, released in 1979, are technically earlier "screen savers". Prior to these computers, games for the 1977 Atari VCS/2600 gaming console such as Combat and Breakout, included color cycling in order to prevent burn-in of game images into 1970s-era televisions. In addition, the first model of the TI-30 calculator from 1976 featured a screensaver, which consisted of a decimal point running across the display after 30 seconds of inactivity. This was chiefly used to save battery power, as the TI-30 LED display was more power intensive than later LCD models. These are examples of screensavers in Read-only memory or the firmware of a computer.
Android 4.2 introduced "daydreams", screensavers that activate while the device is dock connector or charging.
In 2015 the screensaver "Event Listeners" of van den Dorpel became the first work of art that was purchased by a museum (Museum of Applied Arts, Vienna) using the cryptocurrency bitcoin.
Modern graphics technologies such as 3D computer graphics have allowed a wide variety of screensavers to be made. Screensavers with realistic 3D environments can be programmed and run on modern computers.
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