Screensaver
Encyclopedia
Cathode ray tube
The cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen used to view images. It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images. The image may represent electrical waveforms , pictures , radar targets and...
and plasma computer monitors by blanking the screen or filling it with moving images or patterns when the computer is not in use. Contemporary screensavers are used primarily for entertainment or security.
Decades before the first computers utilizing this technology were invented, Robert A. Heinlein
Robert A. Heinlein
Robert Anson Heinlein was an American science fiction writer. Often called the "dean of science fiction writers", he was one of the most influential and controversial authors of the genre. He set a standard for science and engineering plausibility and helped to raise the genre's standards of...
postulated that they would be needed in his novel Stranger In A Strange Land
Stranger in a Strange Land
Stranger in a Strange Land is a 1961 science fiction novel by American author Robert A. Heinlein. It tells the story of Valentine Michael Smith, a human who comes to Earth in early adulthood after being born on the planet Mars and raised by Martians. The novel explores his interaction with—and...
(1961).
Purpose
Before the advent of LCD screens, most computer screens were based on cathode ray tubeCathode ray tube
The cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen used to view images. It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images. The image may represent electrical waveforms , pictures , radar targets and...
s (CRTs). When the same image is displayed on a CRT screen for long periods of time, 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. Cathode ray
Cathode ray
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, the glass opposite of the negative electrode is observed to glow, due to electrons emitted from and travelling perpendicular to the cathode Cathode...
television
Television
Television is a telecommunication medium for transmitting and receiving moving images that can be monochrome or colored, with accompanying sound...
s, oscilloscope
Oscilloscope
An oscilloscope is a type of electronic test instrument that allows observation of constantly varying signal voltages, usually as a two-dimensional graph of one or more electrical potential differences using the vertical or 'Y' axis, plotted as a function of time,...
s and other devices that use CRTs are all susceptible to phosphor burn-in
Phosphor burn-in
Screen burn-in, image burn-in or ghost image, colloquially known as screen burn or screen afterimage, is a permanent discoloration of areas on an electronic display such as a cathode ray tube display or computer display monitor or Television set caused by cumulative non-uniform usage of the...
, as are plasma display
Plasma display
A plasma display panel is a type of flat panel display common to large TV displays or larger. They are called "plasma" displays because the technology utilizes small cells containing electrically charged ionized gases, or what are in essence chambers more commonly known as fluorescent...
s to some extent.
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
Automated teller machine
An automated teller machine or automatic teller machine, also known as a Cashpoint , cash machine or sometimes a hole in the wall in British English, is a computerised telecommunications device that provides the clients of a financial institution with access to financial transactions in a public...
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.
Modern CRTs are much less susceptible to burn-in
Phosphor burn-in
Screen burn-in, image burn-in or ghost image, colloquially known as screen burn or screen afterimage, is a permanent discoloration of areas on an electronic display such as a cathode ray tube display or computer display monitor or Television set caused by cumulative non-uniform usage of the...
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
Laptop
A laptop, also called a notebook, is a personal computer for mobile use. A laptop integrates most of the typical components of a desktop computer, including a display, a keyboard, a pointing device and speakers into a single unit...
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
Image persistence
Image persistence is the LCD and plasma display equivalent of screen burn. Unlike screen burn, however, the effects are usually temporary. Plasma displays can also suffer from burn-in.-Cause:...
). For these reasons, screensavers today are primarily for decorative/entertainment purposes, or for password protection. They usually feature moving images or patterns and sometimes sound effects.
One increasingly popular application is for screensavers to activate a useful background task, such as a virus scan (for example, Avast comes with this feature, and it shows a screensaver [from your computer, you can choose it] with an overlaying blue window showing the progress. If a virus is detected, the window turns red and the scan is stopped, and the alert is shown once you exit the screensaver) or a distributed computing
Distributed computing
Distributed computing is a field of computer science that studies distributed systems. A distributed system consists of multiple autonomous computers that communicate through a computer network. The computers interact with each other in order to achieve a common goal...
application (such as the SETI@home
SETI@home
SETI@home is an Internet-based public volunteer computing project employing the BOINC software platform, hosted by the Space Sciences Laboratory, at the University of California, Berkeley, in the United States. SETI is an acronym for the Search for Extra-Terrestrial Intelligence...
project). This is convenient because these applications use resources only when the computer would be otherwise idle.
Considerations
Monitors running screensavers consume the same amount of power as when running normally, which can be anywhere from a few wattWatt
The watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...
s 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 system
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
s, though it must also be supported by the computer hardware and monitor itself.
Additionally, using a screensaver with a flat panel or LCD
TFT LCD
Thin film transistor liquid crystal display is a variant of liquid crystal display which uses thin-film transistor technology to improve image quality . TFT LCD is one type of Active matrix LCD, though all LCD-screens are based on TFT active matrix addressing...
screen instead of powering down the screen can actually reduce the lifetime of the display, since the fluorescent backlight remains lit and ages faster than it would if the screen was turned off completely. 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, if left on continuously. (In most cases, the tube is an integral part of the LCD and the entire assembly needs to be replaced.)
Thus the term "screen saver" is now something of a misnomer
Misnomer
A misnomer is a term which suggests an interpretation that is known to be untrue. Such incorrect terms sometimes derive their names because of the form, action, or origin of the subject becoming named popularly or widely referenced—long before their true natures were known.- Sources of misnomers...
—the best way to save the screen (and also save electricity) would simply be to have the computer turn off the monitor.
Notice also that screensavers may utilize a significant amount of CPU time, increasing power consumption in the process.
Entertainment
Mathematics
Mathematics is the study of quantity, space, structure, and change. Mathematicians seek out patterns and formulate new conjectures. Mathematicians resolve the truth or falsity of conjectures by mathematical proofs, which are arguments sufficient to convince other mathematicians of their validity...
equations (through the use of fractals) as in the Electric Sheep
Electric Sheep
Electric Sheep is a distributed computing project for animating and evolving fractal flames, which are in turn distributed to the networked computers, which display them as a screensaver.-Process:...
screensaver.
The ability of screensavers to divert and entertain is used for promotion
Promotion (marketing)
Promotion is one of the four elements of marketing mix . It is the communication link between sellers and buyers for the purpose of influencing, informing, or persuading a potential buyer's purchasing decision....
, especially to build buzz
Marketing buzz
Marketing buzz or simply buzz — a term used in word-of-mouth marketing — is the interaction of consumers and users of a product or service which serves to amplify the original marketing message. a vague but positive association, excitement, or anticipation about a product or service...
for "event-based" products such as feature films
Film
A film, also called a movie or motion picture, is a series of still or moving images. It is produced by recording photographic images with cameras, or by creating images using animation techniques or visual effects...
.
The screensaver is also an outlet for the work of creative computer programmers. The Unix
Unix
Unix is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna...
-based screensaver XScreenSaver
XScreenSaver
XScreenSaver is a collection of about two hundred free screensavers for Unix and Mac OS X computers. It was created by Jamie Zawinski in 1992 and is still maintained by him....
collects the display effects of other Unix screensavers, which are termed "display hack
Display hack
A display hack is a computer program with similar purpose to a kaleidoscope: to make pretty pictures . Famous display hacks include munching squares and smoking clover. Some display hacks can be also implemented by creating text files which contain numerous escape sequences for a text terminal to...
s" in the jargon file
Jargon File
The Jargon File is a glossary of computer programmer slang. The original Jargon File was a collection of terms from technical cultures such as the MIT AI Lab, the Stanford AI Lab and others of the old ARPANET AI/LISP/PDP-10 communities, including Bolt, Beranek and Newman, Carnegie Mellon...
tradition of US computer science academics. It also collects forms of computer graphics effects called demo effect
Demo effect
Demo effects are computer-based real-time visual effects found in demos created by the demoscene.The main purpose of demo effects in demos is to show off the skills of the programmer...
s, originally included in demos
Demo (computer programming)
A demo is a non-interactive multimedia presentation made within the computer subculture known as the demoscene. Demogroups create demos to demonstrate their abilities in programming, music, drawing, and 3D modeling...
created by the demo scene.
Security
Password
A password is a secret word or string of characters that is used for authentication, to prove identity or gain access to a resource . The password should be kept secret from those not allowed access....
before permitting the user to resume work. However, a user might be able to circumvent the password by restarting the computer if the computer's owner has set their account to automatically log in upon startup.
Microsoft Windows
On older versions of Microsoft WindowsMicrosoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
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
E-mail attachment
An email attachment is a computer file sent along with an email message. One or more files can be attached to any email message, and be sent along with it to the recipient. This is typically used as a simple method to share documents and images...
, Windows would execute the .scr (screensaver) file automatically: this had the potential to allow a virus or malware
Malware
Malware, short for malicious software, consists of programming that is designed to disrupt or deny operation, gather information that leads to loss of privacy or exploitation, or gain unauthorized access to system resources, or that otherwise exhibits abusive behavior...
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.
In addition, 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
BearShare
BearShare is a peer-to-peer file sharing application originally created by Free Peers, Inc. for Microsoft Windows, and now sold by MusicLab, LLC .- History :...
.
History
The first screensaver was allegedly written for the original IBM PCIBM PC
The IBM Personal Computer, commonly known as the IBM PC, is the original version and progenitor of the IBM PC compatible hardware platform. It is IBM model number 5150, and was introduced on August 12, 1981...
by John Socha
John Socha
John Socha-Leialoha is a software developer best known for creating Norton Commander, the first orthodox file manager. The original Norton Commander was written for DOS...
, best known for creating the Norton Commander
Norton Commander
Norton Commander was a prototypical orthodox file manager , written by John Socha and released by Peter Norton Computing . NC is a file manager which provides a text user interface on top of DOS. It was officially produced by Symantec between 1986 and 1998...
; he also coined the term screen saver. The screensaver, named scrnsave, was published in December 1983 issue of the Softalk
Softalk
Softalk was a magazine of the early 1980s that focused on the Apple II computer. Published from 1979 through 1984, it featured articles about hardware and software associated with the Apple II platform and the people and companies who made them...
magazine. It simply blanked the screen after three minutes of inactivity (an interval which could be changed only by recompiling the program).
The first screensaver that allowed users to change the activating time was released on Apple
Apple Computer
Apple Inc. is an American multinational corporation that designs and markets consumer electronics, computer software, and personal computers. The company's best-known hardware products include the Macintosh line of computers, the iPod, the iPhone and the iPad...
's Lisa
Apple Lisa
The Apple Lisa—also known as the Lisa—is a :personal computer designed by Apple Computer, Inc. during the early 1980s....
, in 1983.
The Atari 400 and 800's screens would also go through random screensaver-like color changes if they were left inactive for too long. The user had no control over this. 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 1970's-era televisions. These are examples of screensavers in ROM
Read-only memory
Read-only memory is a class of storage medium used in computers and other electronic devices. Data stored in ROM cannot be modified, or can be modified only slowly or with difficulty, so it is mainly used to distribute firmware .In its strictest sense, ROM refers only...
or the firmware
Firmware
In electronic systems and computing, firmware is a term often used to denote the fixed, usually rather small, programs and/or data structures that internally control various electronic devices...
of a computer.
Today with the help of modern graphics technologies there is a wide variety of different screensavers. Because of 3D computer graphics
3D computer graphics
3D computer graphics are graphics that use a three-dimensional representation of geometric data that is stored in the computer for the purposes of performing calculations and rendering 2D images...
, 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 CC (programming language)
C is a general-purpose computer programming language developed between 1969 and 1973 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system....
or C++
C++
C++ is a statically typed, free-form, multi-paradigm, compiled, general-purpose programming language. It is regarded as an intermediate-level language, as it comprises a combination of both high-level and low-level language features. It was developed by Bjarne Stroustrup starting in 1979 at Bell...
programming languages, along with Graphics Device Interface
Graphics Device Interface
The Graphics Device Interface is a Microsoft Windows application programming interface and core operating system component responsible for representing graphical objects and transmitting them to output devices such as monitors and printers....
(GDI), DirectX
DirectX
Microsoft DirectX is a collection of application programming interfaces for handling tasks related to multimedia, especially game programming and video, on Microsoft platforms. Originally, the names of these APIs all began with Direct, such as Direct3D, DirectDraw, DirectMusic, DirectPlay,...
, or OpenGL
OpenGL
OpenGL is a standard specification defining a cross-language, cross-platform API for writing applications that produce 2D and 3D computer graphics. The interface consists of over 250 different function calls which can be used to draw complex three-dimensional scenes from simple primitives. OpenGL...
, to craft their final products. Several Mac OS X
Mac OS X
Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...
screensavers are created and designed using the Quartz Extreme graphics layer. 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.