Screensaver

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World Community Grid screensaver that uses idle system resources to help analyze proteins. Screensaver HUMAN PROTEOME FOLDING Phase2.png
World Community Grid screensaver that uses idle system resources to help analyze proteins.

A screensaver (or screen saver) is a computer program that blanks the screen or fills it with moving images or patterns when the computer is not in use. The original purpose of screensavers was to prevent phosphor burn-in on CRT and plasma computer monitors (hence the name). Though modern monitors are not susceptible to this issue, screensavers are still used for other purposes. Screensavers are often set up to offer a basic layer of security, by requiring a password to re-access the device. Some screensavers use the otherwise unused computer resources to do useful work, such as processing for distributed computing projects.

Computer program Instructions to be executed by a computer

A computer program is a collection of instructions that performs a specific task when executed by a computer. A computer requires programs to function.

Screen burn-in

Screen burn-in, image burn-in or ghost image, colloquially known as screen burn or ghosting, is a discoloration of areas on an electronic display such as a CRT display or an old computer monitor or television set caused by cumulative non-uniform use of the pixels. For newer displays like LCD monitors, they may suffer from a phenomenon called image persistence instead, which is not permanent.

Computer monitor electronic visual display for computers

A computer monitor is an output device that displays information in pictorial form. A monitor usually comprises the display device, circuitry, casing, and power supply. The display device in modern monitors is typically a thin film transistor liquid crystal display (TFT-LCD) with LED backlighting having replaced cold-cathode fluorescent lamp (CCFL) backlighting. Older monitors used a cathode ray tube (CRT). Monitors are connected to the computer via VGA, Digital Visual Interface (DVI), HDMI, DisplayPort, Thunderbolt, low-voltage differential signaling (LVDS) or other proprietary connectors and signals.

Contents

As well as computers, modern television operating systems, media players and other digital entertainment systems include optional screensavers.

Purpose

Screen protection

Before the advent of LCD screens, most computer screens were based on cathode ray tubes (CRTs). When the same image is displayed on a CRT screen for long periods, the properties of the exposed areas of phosphor coating on the inside of the screen gradually and permanently change, eventually leading to a darkened shadow or "ghost" image on the screen, called a screen burn-in. Cathode ray televisions, oscilloscopes and other devices that use CRTs are all susceptible to phosphor burn-in, as are plasma displays to some extent.

Cathode ray stream of electrons observed in vacuum tubes

Cathode rays are streams of electrons observed in vacuum tubes. If an evacuated glass tube is equipped with two electrodes and a voltage is applied, glass behind the positive electrode is observed to glow, due to electrons emitted from the cathode. They were first observed in 1869 by German physicist Julius Plücker and Johann Wilhelm Hittorf, and were named in 1876 by Eugen Goldstein Kathodenstrahlen, or cathode rays. In 1897, British physicist J. J. Thomson showed that cathode rays were composed of a previously unknown negatively charged particle, which was later named the electron. Cathode ray tubes (CRTs) use a focused beam of electrons deflected by electric or magnetic fields to render an image on a screen.

Television Telecommunication medium for transmitting and receiving moving images

Television (TV), sometimes shortened to tele or telly, is a telecommunication medium used for transmitting moving images in monochrome, or in color, and in two or three dimensions and sound. The term can refer to a television set, a television program, or the medium of television transmission. Television is a mass medium for advertising, entertainment and news.

Oscilloscope type of electronic test instrument

An oscilloscope, previously called an oscillograph, and informally known as a scope or o-scope, CRO, or DSO, is a type of electronic test instrument that graphically displays varying signal voltages, usually as a two-dimensional plot of one or more signals as a function of time. Other signals can be converted to voltages and displayed.

Screen-saver programs were designed to help avoid these effects by automatically changing the images on the screen during periods of user inactivity.

For CRTs used in public, such as ATMs and railway ticketing machines, 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 out of the question as the machine would appear to be 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.

Automated teller machine electronic banking kiosk

An automated teller machine (ATM) is an electronic telecommunications device that enables customers of financial institutions to perform financial transactions, such as cash withdrawals, deposits, transfer funds, or obtaining account information, at any time and without the need for direct interaction with bank staff.

Modern CRTs are much less susceptible to burn-in than older models due to improvements in phosphor coatings, and because modern computer images are generally lower contrast than the stark green- or white-on-black text and graphics of earlier machines. 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).

Laptop personal computer for mobile use

A laptop computer is a small, portable personal computer (PC) with a "clamshell" form factor, typically having a thin LCD or LED computer screen mounted on the inside of the upper lid of the clamshell and an alphanumeric keyboard on the inside of the lower lid. The clamshell is opened up to use the computer. Laptops are folded shut for transportation, and thus are suitable for mobile use. Its name comes from lap, as it was deemed to be placed on a person's lap when being used. Although originally there was a distinction between laptops and notebooks, as of 2014, there is often no longer any difference. Laptops are commonly used in a variety of settings, such as at work, in education, for playing games, Internet surfing, for personal multimedia, and general home computer use.

Image persistence

Image persistence, or image retention, is the LCD and plasma display equivalent of screen burn. Unlike screen burn, the effects are usually temporary and often times not visible without close inspection. Plasma displays experiencing severe image persistence can result in screen burn-in instead.

Modern usage

Gnome-screensaver has an option for password protection Gnome-screensaver.png
Gnome-screensaver has an option for password protection

While modern screens are not susceptible to the issues discussed above, screensavers are still used. Primarily these are for decorative/entertainment purposes, or for password protection. They usually feature moving images or patterns and sometimes sound effects.

As screensavers are generally expected to activate when users are away from their machines, many screensavers can be configured to ask users for a password before permitting the user to resume work. This is a basic security measure against another person accessing the machine while the user is absent.

Password used for user authentication to prove identity or access approval

A password is a word or string of characters used for user authentication to prove identity or access approval to gain access to a resource, which is to be kept secret from those not allowed access.

Some screensavers activate a useful background task, such as a virus scan or a distributed computing application (such as the SETI@home project). This allows applications to use resources only when the computer would be otherwise idle.

Distributed computing is a field of computer science that studies distributed systems. A distributed system is a system whose components are located on different networked computers, which communicate and coordinate their actions by passing messages to one another. The components interact with one another in order to achieve a common goal. Three significant characteristics of distributed systems are: concurrency of components, lack of a global clock, and independent failure of components. Examples of distributed systems vary from SOA-based systems to massively multiplayer online games to peer-to-peer applications.

SETI@home is an Internet-based public volunteer computing project employing the BOINC software platform created by the Berkeley SETI Research Center and is hosted by the Space Sciences Laboratory, at the University of California, Berkeley. Its purpose is to analyze radio signals, searching for signs of extraterrestrial intelligence, and as such is one of many activities undertaken as part of the worldwide SETI effort.

History

Decades before the first computers using this technology were invented, Robert A. Heinlein gave an example of how they might be used in his novel Stranger In A Strange Land (1961): [1] [2]

Opposite his chair was a stereovision tank disguised as an aquarium; he switched it on, guppies and tetras gave way to the face of the well-known Winchell Augustus Greaves.

The first screensaver was allegedly written for the original IBM PC by John Socha, best known for creating the 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 (an interval which could be changed only by recompiling the program).

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". [3] The first screensaver that allowed users to change the activating time was released on Apple's 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." And prior to these computers, the 1977 Atari VCS/2600 gaming console included color cycling in games like Combat or Breakout, in order to prevent burn-in of game images to 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 LED display was more power intensive than later LCD models. These are examples of screensavers in ROM or the firmware of a computer.

Today with the help of modern graphics technologies there is a wide variety of screensavers. Because of 3D computer graphics, which provide realistic environments, 3D screensavers are available.

Underlying architecture

Screensavers are usually designed and coded using a variety of programming languages as well as graphics interfaces. Typically the authors of screensavers use the C or C++ programming languages, along with Graphics Device Interface (GDI), DirectX, or OpenGL, to craft their final products. Several OS X screensavers are created and designed using Quartz Composer. The screensaver interfaces indirectly with the operating system to cause the physical display screen to be overlaid with one or more graphic "scenes". The screensaver typically terminates after receiving a message from the operating system that a key has been pressed or the mouse has been moved.

Microsoft Windows

If the system detects inactivity lasting longer than the time specified in the control panel, check if the active program is a simple program (and not another screensaver) by sending the "WM_SYSCOMMAND message" with the "SC_SCREENSAVE" argument. If the program calls in response the standard system function (DefWindowProc), the screensaver defined in the control panel screen runs.

A Windows screensaver is a regular Portable Executable (PE) with the .scr file extension. In addition, this program should support the following command line parameters: [4]

With no parameter – shows the Settings dialog box or do nothing.

ScreenSaver.scr /s

Runs the screensaver.

ScreenSaver.scr /p or /l <HWND>

Previews the screensaver as child of window. <HWND> (presented as unsigned decimal number) is an identifier (handle) of the window in which to appear preview.

ScreenSaver.scr /c

Shows the Settings dialog box, modal to the foreground window.

ScreenSaver.scr /a <HWND>

Changes password, modal to window <HWND>. Windows 95 screensavers must handle it.

MacOS

Under MacOS, screensavers are regular MacOS application bundles with the .saver file extension [5] .

Internally, the screensaver must define a class that is subclass of ScreenSaverView. The new class must be assigned as NSPrincipalClass in the xcode project, so that when the screensaver is launched by the system, this class gets instantiated.

Atari

As one of the first screensavers appeared in 8-bit Atari computers, forcing systemic color changes when the computer is idle lasting a few minutes (different times depending on the model), stored in the system ROM of the computer.

Considerations

Monitors running screensavers consume the same amount of power as when running normally, which can be anywhere from a few watts for small LCD monitors to several hundred for large plasma displays. Most modern computers can be set to switch the monitor into a lower power mode, blanking the screen altogether. A power-saving mode for monitors is usually part of the power management options supported in most modern operating systems, though it must also be supported by the computer hardware and monitor itself.

Using a screensaver with a flat panel or 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. [6] [7] . 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.

Entertainment

XScreenSaver displaying a Matrix-style screensaver Xscreensaver xmatrix.png
XScreenSaver displaying a Matrix-style screensaver

After Dark was an early screensaver for the Macintosh platform, and later PC/Windows, which prominently featured whimsical designs such as flying toasters. Perhaps in response to the workplace environment in which they are often viewed, many screensavers continue this legacy of whimsy by populating the idle monitor with animals or fish, games, and visual expressions of mathematics equations (through the use of fractals, Fourier transforms or other means) as in the Electric Sheep screensaver.

At least one screensaver, Johnny Castaway told a humorous animated story over many months. [8] The ability of screensavers to divert and entertain is used for promotion, especially to build buzz for "event-based" products such as feature films.

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 demo effects , originally included in demos created by the demo scene.

Microsoft Windows

On older versions of Microsoft Windows the native screensaver format had the potential to install a virus when run (as a screen saver was just an ordinary application with a different extension). When any file with the file suffix ".scr" was opened, for example from an e-mail attachment, Windows would execute the .scr (screensaver) file automatically: this had the potential to allow a virus or malware to install itself. Modern versions of Windows can read tags left by applications such as Internet Explorer and verify the publisher of the file, presenting a confirmation to the user.

On August 5, 2006, the BBC reported that "free screensavers" and "screensavers" respectively were the first and third most likely search terms to return links to malware, the second being BearShare. [9]

See also

Related Research Articles

Cathode-ray tube vacuum tube that can show moving pictures, vector graphics, or lines

The cathode-ray tube (CRT) is a vacuum tube that contains one or more electron guns and a phosphorescent screen, and is used to display images. It modulates, accelerates, and deflects electron beam(s) onto the screen to create the images. The images may represent electrical waveforms (oscilloscope), pictures, radar targets, or other phenomena. CRTs have also been used as memory devices, in which case the visible light emitted from the fluorescent material is not intended to have significant meaning to a visual observer.

Framebuffer portion of RAM containing a bitmap that drives a video display

A framebuffer is a portion of RAM containing a bitmap that drives a video display. It is a memory buffer containing a complete frame of data. Modern video cards contain framebuffer circuitry in their cores. This circuitry converts an in-memory bitmap into a video signal that can be displayed on a computer monitor.

Light-on-dark color scheme color scheme

Light-on-dark color scheme, also called dark mode, dark theme or night mode, is a color scheme that uses light-colored text, icons, and graphical user interface elements on a dark background and is often discussed in terms of computer user interface design and web design.

A plasma display panel (PDP) is a type of flat panel display that uses small cells containing plasma; ionized gas that responds to electric fields.

XScreenSaver Screensaversoftware for system using the X Window system

XScreenSaver is a collection of 229 free screensavers for Unix, macOS, iOS and Android. It was created by Jamie Zawinski in 1992 and is still maintained by him.

The refresh rate is the number of times in a second that a display hardware updates its buffer. This is distinct from the measure of frame rate. The refresh rate includes the repeated drawing of identical frames, while frame rate measures how often a video source can feed an entire frame of new data to a display.

Display resolution how many pixels a monitor can display

The display resolution or display modes of a digital television, computer monitor or display device is the number of distinct pixels in each dimension that can be displayed. It can be an ambiguous term especially as the displayed resolution is controlled by different factors in cathode ray tube (CRT) displays, flat-panel displays and projection displays using fixed picture-element (pixel) arrays.

Flicker is a visible change in brightness between cycles displayed on video displays. It applies especially to the refresh interval on Cathode ray tube (CRT) televisions and computer monitors, as well as Plasma based computer screens and televisions.

Screen Savers or screensaver or variation, may refer to:

Storage tube

Storage tubes are a class of cathode-ray tubes (CRTs) that are designed to hold an image for a long period of time, typically as long as power is supplied to the tube.

An output device is any piece of computer hardware equipment which converts information into human-readable form.

Active shutter 3D system

An active shutter 3D system is a technique of displaying stereoscopic 3D images. It works by only presenting the image intended for the left eye while blocking the right eye's view, then presenting the right-eye image while blocking the left eye, and repeating this so rapidly that the interruptions do not interfere with the perceived fusion of the two images into a single 3D image.

Matrix digital rain

Matrix digital rain, Matrix code or sometimes green rain, is the computer code featured in the Matrix series. The falling green code is a way of representing the activity of the virtual reality environment of the Matrix on screen. All three Matrix movies, as well as the spin-off The Animatrix episodes, open with the code. It is a characteristic mark of the franchise, similar to the opening crawl in Star Wars.

Large-screen television technology

Large-screen television technology developed rapidly in the late 1990s and 2000s. Various thin screen technologies are being developed, but only the liquid crystal display (LCD), plasma display (PDP) and Digital Light Processing (DLP) have been released on the public market. A video display that uses large-screen television technology is called a jumbotron. These technologies have almost completely displaced cathode ray tubes (CRT) in television sales, due to the necessary bulkiness of cathode ray tubes. However, recently released technologies like organic light-emitting diode (OLED) and not-yet released technologies like surface-conduction electron-emitter display (SED) or field emission display (FED) are making their way to replace the first flat screen technologies in picture quality. The diagonal screen size of a CRT television is limited to about 40 inches because of the size requirements of the cathode ray tube, which fires three beams of electrons onto the screen, creating a viewable image. A larger screen size requires a longer tube, making a CRT television with a large screen unrealistic because of size. The aforementioned technologies can produce large-screen televisions that are much thinner.

Vector monitor

A vector monitor or vector display is a display device used for computer graphics up through the 1970s. It is a type of CRT, similar to that of an early oscilloscope. In a vector display, the image is composed of drawn lines rather than a grid of glowing pixels as in raster graphics. The electron beam follows an arbitrary path tracing the connected sloped lines, rather than following the same horizontal raster path for all images. The beam skips over dark areas of the image without visiting their points.

Display motion blur, also called HDTV blur and LCD motion blur, refers to several visual artifacts that are frequently found on modern consumer high-definition television sets and flat panel displays for computers.

Monochrome monitor CRT computer display

A monochrome monitor is a type of CRT computer monitor which was very common in the early days of computing, from the 1960s through the 1980s, before color monitors became popular. They are still widely used in applications such as computerized cash register systems, owing to the age of many registers. Green screen was the common name for a monochrome monitor using a green "P1" phosphor screen.

References

  1. Screensaver (Inventor of) by Robert Heinlein from Stranger in a Strange Land Archived March 18, 2015, at the Wayback Machine
  2. Heinlein, Robert (1987). Stranger in a Strange Land. New York, NY: Penguin. p. 448. ISBN   9780441790340.
  3. Chin, Kathy (1983-04-11). "Z-29, a new computer terminal from Zenith Data Systems". InfoWorld. InfoWorld Media Group, Inc. p. 13. Retrieved 2017-08-13.
  4. "INFO: Screen Saver Command Line Arguments". Microsoft.
  5. "ScreenSaverView - ScreenSaver | Apple Developer Documentation". developer.apple.com. Retrieved 2018-09-25.
  6. https://web.archive.org/web/20111028205846/http://www.cbc.ca/quirks/episode/2011/10/22/october-22-2011
  7. https://www.energy.gov/energysaver/save-electricity-and-fuel/lighting-choices-save-you-money/when-turn-your-lights
  8. Emrich, Alan; Wilson, Johnny L. (January 1993). "The Misadventures of Johnny Castaway". Computer Gaming World. p. 16. Retrieved 5 July 2014.
  9. "Warning on search engine safety". BBC News. 2006-05-12. Retrieved 2010-06-07.