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In 1984, the first IBM PCjr had a rudimentary 3-voice sound synthesis chip which was capable of generating three square-wave tones with variable amplitude, and a pseudo-white noise channel that could generate primitive percussion sounds. The Tandy 1000, initially a clone of the PCjr, duplicated this functionality, with the Tandy 1000 TL/SL/RL models adding digital sound recording and playback capabilities. Many games during the 1980s that supported the PCjr's video standard also supported PCjr/Tandy 1000 audio.
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5,002
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In the late 1990s, many computer manufacturers began to replace plug-in sound cards with an audio codec chip integrated into the motherboard. Many of these used Intel's AC'97 specification. Others used inexpensive ACR slot accessory cards.
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5,003
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From around 2001, many motherboards incorporated full-featured sound cards, usually in the form of a custom chipset, providing something akin to full Sound Blaster compatibility and relatively high-quality sound. However, these features were dropped when AC'97 was superseded by Intel's HD Audio standard, which was released in 2004, again specified the use of a codec chip, and slowly gained acceptance. As of 2011, most motherboards have returned to using a codec chip, albeit an HD Audio compatible one, and the requirement for Sound Blaster compatibility relegated to history.
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5,004
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Various non-IBM PC compatible computers, such as early home computers like the Commodore 64 and Amiga , NEC's PC-88, Fujitsu's FM-7 and FM Towns, Sharp's X1 and X68000, Acorn's BBC Micro, Electron and Archimedes, Atari's 8-bit home computers, ST and Falcon, Amstrad's CPC, later revisions of Sinclair's ZX Spectrum, the MSX, Apple's Macintosh and IIGS, and workstations from manufacturers like Sun, Silicon Graphics and NeXT have had their own motherboard-integrated sound devices. In some cases, most notably in those of the Macintosh, IIGS, Amiga, C64, SGI Indigo, X68000, MSX, Falcon, Archimedes, FM-7 and FM Towns, they provide very advanced capabilities , in others they are only minimal capabilities. Some of these platforms have also had sound cards designed for their bus architectures that cannot be used in a standard PC.
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5,005
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Several Japanese computer platforms, including the MSX, X1, X68000, FM Towns and FM-7, featured built-in FM synthesis sound from Yamaha by the mid-1980s. By 1989, the FM Towns computer platform featured built-in PCM sample-based sound and supported the CD-ROM format.
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5,006
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The custom sound chip on Amiga, named Paula, had four digital sound channels with 8-bit resolution for each channel and a 6-bit volume control per channel. Sound playback on Amiga was done by reading directly from the chip RAM without using the main CPU.
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5,007
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Most arcade games have integrated sound chips, the most popular being the Yamaha OPL chip for music coupled with a variety of DACs for sampled audio and sound effects.
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5,008
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The earliest known sound card used by computers was the Gooch Synthetic Woodwind, a music device for PLATO terminals, and is widely hailed as the precursor to sound cards and MIDI. It was invented in 1972.
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5,009
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Certain early arcade machines made use of sound cards to achieve playback of complex audio waveforms and digital music, despite being already equipped with onboard audio. An example of a sound card used in arcade machines is the Digital Compression System card, used in games from Midway. For example, Mortal Kombat II on the Midway T-Unit hardware. The T-Unit hardware already has an onboard YM2151 OPL chip coupled with an OKI 6295 DAC, but said game uses an added-on DCS card instead. The card is also used in the arcade version of Midway and Aerosmith's Revolution X for complex looping music and speech playback.
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5,010
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MSX computers, while equipped with built-in sound capabilities, also relied on sound cards to produce better quality audio. The card, known as Moonsound, uses a Yamaha OPL4 sound chip. Prior to the Moonsound, there were also sound cards called MSX Music and MSX Audio for the system, which uses OPL2 and OPL3 chipsets.
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5,011
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The Apple II computers, which did not have sound capabilities beyond rapidly clicking a speaker until the IIGS, could use plug-in sound cards from a variety of manufacturers. The first, in 1978, was ALF's Apple Music Synthesizer, with 3 voices; two or three cards could be used to create 6 or 9 voices in stereo. Later ALF created the Apple Music II, a 9-voice model. The most widely supported card, however, was the Mockingboard. Sweet Micro Systems sold the Mockingboard in various models. Early Mockingboard models ranged from 3 voices in mono, while some later designs had 6 voices in stereo. Some software supported use of two Mockingboard cards, which allowed 12-voice music and sound. A 12-voice, single-card clone of the Mockingboard called the Phasor was made by Applied Engineering.
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5,012
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The ZX Spectrum that initially only had a beeper had some sound cards made for it. Examples include TurboSound Other examples are the Fuller Box, and Zon X-81.
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5,013
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The Commodore 64, while having an integrated SID chip, also had sound cards made for it. For example, the Sound Expander, which added on an OPL FM synthesizer.
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5,014
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The PC-98 series of computers, like their IBM PC cousins, also do not have integrated sound contrary to popular belief, and their default configuration is a PC speaker driven by a timer. Sound cards were made for the C-Bus expansion slots that these computers had, most of which used Yamaha's FM and PSG chips and made by NEC themselves, although aftermarket clones can also be purchased, and Creative did release a C-Bus version of the SoundBlaster line of sound cards for the platform.
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5,015
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Devices such as the Covox Speech Thing could be attached to the parallel port of an IBM PC and fed 6- or 8-bit PCM sample data to produce audio. Also, many types of professional sound cards take the form of an external FireWire or USB unit, usually for convenience and improved fidelity.
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5,016
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Sound cards using the PC Card interface were available before laptop and notebook computers routinely had onboard sound. Most of these units were designed for mobile DJs, providing separate outputs to allow both playback and monitoring from one system, however, some also target mobile gamers.
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5,017
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USB sound cards are external devices that plug into the computer via USB. They are often used in studios and on stage by electronic musicians including live PA performers and DJs. DJs who use DJ software typically use sound cards integrated into DJ controllers or specialized DJ sound cards. DJ sound cards sometimes have inputs with phono preamplifiers to allow turntables to be connected to the computer to control the software's playback of music files with vinyl emulation.
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5,018
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The USB specification defines a standard interface, the USB audio device class, allowing a single driver to work with the various USB sound devices and interfaces on the market. Mac OS X, Windows, and Linux support this standard. However, some USB sound cards do not conform to the standard and require proprietary drivers from the manufacturer.
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5,019
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Cards meeting the older USB 1.1 specification are capable of high-quality sound with a limited number of channels, but USB 2.0 or later is more capable with their higher bandwidths.
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5,020
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The main function of a sound card is to play audio, usually music, with varying formats and degrees of control. The source may be a CD or DVD, a file, streamed audio, or any external source connected to a sound card input. Audio may be recorded. Sometimes sound card hardware and drivers do not support recording a source that is being played.
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5,021
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Sound cards can be used to generate arbitrary electrical waveforms, as any digital waveform played by the soundcard is converted to the desired output within the bounds of its capabilities. In other words, sound cards are consumer-grade arbitrary waveform generators. A number of free and commercial software allow sound cards to act like function generators by generating desired waveforms from functions; there are also online services that generate audio files for any desired waveforms, playable through a sound card.
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5,022
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Sound cards can also be used to record electrical waveforms, in the same way it records an analog audio input. The recording can be displayed by special or general-purpose audio-editing software or further transformed and analyzed. A protection circuit should be used to keep the input voltage within acceptable bounds.
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5,023
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As general-purpose waveform generators and analyzers, sound cards are bound by several design and physical limitations.
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5,024
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Sound cards have been used to analyze and generate the following types of signals:
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5,025
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To use a sound card, the operating system typically requires a specific device driver, a low-level program that handles the data connections between the physical hardware and the operating system. Some operating systems include the drivers for many cards; for cards not so supported, drivers are supplied with the card, or available for download.
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5,026
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The most common type of projector used today is called a video projector. Video projectors are digital replacements for earlier types of projectors such as slide projectors and overhead projectors. These earlier types of projectors were mostly replaced with digital video projectors throughout the 1990s and early 2000s, but old analog projectors are still used at some places. The newest types of projectors are handheld projectors that use lasers or LEDs to project images.
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5,027
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Movie theaters used a type of projector called a movie projector, nowadays mostly replaced with digital cinema video projectors.
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5,028
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Projectors can be roughly divided into three categories, based on the type of input. Some of the listed projectors were capable of projecting several types of input. For instance: video projectors were basically developed for the projection of prerecorded moving images, but are regularly used for still images in PowerPoint presentations and can easily be connected to a video camera for real-time input. The magic lantern is best known for the projection of still images, but was capable of projecting moving images from mechanical slides since its invention and was probably at its peak of popularity when used in phantasmagoria shows to project moving images of ghosts.
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5,029
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There probably existed quite a few other types of projectors than the examples described below, but evidence is scarce and reports are often unclear about their nature. Spectators did not always provide the details needed to differentiate between for instance a shadow play and a lantern projection. Many did not understand the nature of what they had seen and few had ever seen other comparable media. Projections were often presented or perceived as magic or even as religious experiences, with most projectionists unwilling to share their secrets. Joseph Needham sums up some possible projection examples from China in his 1962 book series Science and Civilization in China
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5,030
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The earliest projection of images was most likely done in primitive shadowgraphy dating back to prehistory. Shadow play usually does not involve a projection device, but can be seen as a first step in the development of projectors. It evolved into more refined forms of shadow puppetry in Asia, where it has a long history in Indonesia , Malaysia, Thailand, Cambodia, China , India and Nepal.
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5,031
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Projectors share a common history with cameras in the camera obscura. Camera obscura is the natural optical phenomenon that occurs when an image of a scene at the other side of a screen is projected through a small hole in that screen to form an inverted image on a surface opposite to the opening. The oldest known record of this principle is a description by Han Chinese philosopher Mozi . Mozi correctly asserted that the camera obscura image is inverted because light travels in straight lines.
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5,032
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In the early 11th century, Arab physicist Ibn al-Haytham described experiments with light through a small opening in a darkened room and realized that a smaller hole provided a sharper image.
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5,033
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The oldest known objects that can project images are Chinese magic mirrors. The origins of these mirrors have been traced back to the Chinese Han dynasty and are also found in Japan. The mirrors were cast in bronze with a pattern embossed at the back and a mercury amalgam laid over the polished front. The pattern on the back of the mirror is seen in a projection when light is reflected from the polished front onto a wall or other surface. No trace of the pattern can be discerned on the reflecting surface with the naked eye, but minute undulations on the surface are introduced during the manufacturing process and cause the reflected rays of light to form the pattern. It is very likely that the practice of image projection via drawings or text on the surface of mirrors predates the very refined ancient art of the magic mirrors, but no evidence seems to be available.
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5,034
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Revolving lanterns have been known in China as "trotting horse lamps" since before 1000 CE. A trotting horse lamp is a hexagonal, cubical or round lantern which on the inside has cut-out silhouettes attached to a shaft with a paper vane impeller on top, rotated by heated air rising from a lamp. The silhouettes are projected on the thin paper sides of the lantern and appear to chase each other. Some versions showed some extra motion in the heads, feet and/or hands of figures by connecting them with a fine iron wire to an extra inner layer that would be triggered by a transversely connected iron wire. The lamp would typically show images of horses and horse-riders.
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5,035
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In France, similar lanterns were known as "lanterne vive" in Medieval times. and as "lanterne tournante" since the 18th century. An early variation was described in 1584 by Jean Prevost in his small octavo book La Premiere partie des subtiles et plaisantes inventions. In his "lanterne", cut-out figures of a small army were placed on a wooden platform rotated by a cardboard propeller above a candle. The figures cast their shadows on translucent, oiled paper on the outside of the lantern. He suggested to take special care that the figures look lively: with horses raising their front legs as if they were jumping and soldiers with drawn swords, a dog chasing a hare, etcetera. According to Prevost barbers were skilled in this art and it was common to see these night lanterns in their shop windows.
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5,036
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A more common version had the figures, usually representing grotesque or devilish creatures, painted on a transparent strip. The strip was rotated inside a cylinder by a tin impeller above a candle. The cylinder could be made of paper or of sheet metal perforated with decorative patterns. Around 1608 Mathurin Régnier mentioned the device in his Satire XI as something used by a patissier to amuse children. Régnier compared the mind of an old nagger with the lantern's effect of birds, monkeys, elephants, dogs, cats, hares, foxes and many strange beasts chasing each other.
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5,037
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John Locke referred to a similar device when wondering if ideas are formed in the human mind at regular intervals,"not much unlike the images in the inside of a lantern, turned round by the heat of a candle." Related constructions were commonly used as Christmas decorations in England and parts of Europe. A still relatively common type of rotating device that is closely related does not really involve light and shadows, but it simply uses candles and an impeller to rotate a ring with tiny figurines standing on top.
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5,038
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Many modern electric versions of this type of lantern use all kinds of colorful transparent cellophane figures which are projected across the walls, especially popular for nurseries.
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5,039
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The inverted real image of an object reflected by a concave mirror can appear at the focal point in front of the mirror. In a construction with an object at the bottom of two opposing concave mirrors on top of each other, the top one with an opening in its center, the reflected image can appear at the opening as a very convincing 3D optical illusion.
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5,040
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The earliest description of projection with concave mirrors has been traced back to a text by French author Jean de Meun in his part of Roman de la Rose . A theory known as the Hockney-Falco thesis claims that artists used either concave mirrors or refractive lenses to project images onto their canvas/board as a drawing/painting aid as early as circa 1430.
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5,041
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It has also been thought that some encounters with spirits or gods since antiquity may have been conjured up with mirrors.
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5,042
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Around 1420 the Venetian scholar and engineer Giovanni Fontana included a drawing of a person with a lantern projecting an image of a demon in his book about mechanical instruments "Bellicorum Instrumentorum Liber". The Latin text "Apparentia nocturna ad terrorem videntium" " clarifies its purpose, but the meaning of the undecipherable other lines is unclear. The lantern seems to simply have the light of an oil lamp or candle go through a transparent cylindrical case on which the figure is drawn to project the larger image, so it probably couldn't project an image as clearly defined as Fontana's drawing suggests.
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5,043
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In 1437 Italian humanist author, artist, architect, poet, priest, linguist, philosopher and cryptographer Leon Battista Alberti is thought to have possibly projected painted pictures from a small closed box with a small hole, but it is unclear whether this actually was a projector or rather a type of show box with transparent pictures illuminated from behind and viewed through the hole.
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5,044
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Leonardo da Vinci is thought to have had a projecting lantern - with a condensing lens, candle and chimney - based on a small sketch from around 1515.
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5,045
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In his Three Books of Occult Philosophy Heinrich Cornelius Agrippa claimed that it was possible to project "images artificially painted, or written letters" onto the surface of the Moon with the means of moonbeams and their "resemblances being multiplied in the air". Pythagoras would have often performed this trick.
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5,046
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In 1589 Giambattista della Porta published about the ancient art of projecting mirror writing in his book Magia Naturalis.
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5,047
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Dutch inventor Cornelis Drebbel, who is a likely inventor of the microscope, is thought to have had some kind of projector that he used in magical performances. In a 1608 letter he described the many marvelous transformations he performed and the apparitions that he summoned by the means of his new invention based on optics. It included giants that rose from the earth and moved all their limbs very lifelike. The letter was found in the papers of his friend Constantijn Huygens, father of the likely inventor of the magic lantern Christiaan Huygens.
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5,048
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In 1612 Italian mathematician Benedetto Castelli wrote to his mentor, the Italian astronomer, physicist, engineer, philosopher and mathematician Galileo Galilei about projecting images of the sun through a telescope to study the recently discovered sunspots. Galilei wrote about Castelli's technique to the German Jesuit priest, physicist and astronomer Christoph Scheiner.
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5,049
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From 1612 to at least 1630 Christoph Scheiner would keep on studying sunspots and constructing new telescopic solar projection systems. He called these "Heliotropii Telioscopici", later contracted to helioscope.
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5,050
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The 1645 first edition of German Jesuit scholar Athanasius Kircher's book Ars Magna Lucis et Umbrae included a description of his invention, the steganographic mirror: a primitive projection system with a focusing lens and text or pictures painted on a concave mirror reflecting sunlight, mostly intended for long distance communication. He saw limitations in the increase of size and diminished clarity over a long distance and expressed his hope that someone would find a method to improve on this. Kircher also suggested projecting live flies and shadow puppets from the surface of the mirror. The book was quite influential and inspired many scholars, probably including Christiaan Huygens who would invent the magic lantern. Kircher was often credited as the inventor of the magic lantern, although in his 1671 edition of Ars Magna Lucis et Umbrae Kircher himself credited Danish mathematician Thomas Rasmussen Walgensten for the magic lantern, which Kircher saw as a further development of his own projection system.
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5,051
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Although Athanasius Kircher claimed the Steganographic mirror as his own invention and wrote not to have read about anything like it, it has been suggested that Rembrandt's 1635 painting of "Belshazzar's Feast" depicts a steganographic mirror projection with God's hand writing Hebrew letters on a dusty mirror's surface.
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5,052
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In 1654 Belgian Jesuit mathematician André Tacquet used Kircher's technique to show the journey from China to Belgium of Italian Jesuit missionary Martino Martini. It is sometimes reported that Martini lectured throughout Europe with a magic lantern which he might have imported from China, but there's no evidence that anything other than Kircher's technique was used.
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5,053
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By 1659 Dutch scientist Christiaan Huygens had developed the magic lantern, which used a concave mirror to reflect and direct as much of the light of a lamp as possible through a small sheet of glass on which was the image to be projected, and onward into a focusing lens at the front of the apparatus to project the image onto a wall or screen . He did not publish nor publicly demonstrate his invention as he thought it was too frivolous.
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5,054
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The magic lantern became a very popular medium for entertainment and educational purposes in the 18th and 19th century. This popularity waned after the introduction of cinema in the 1890s. The magic lantern remained a common medium until slide projectors came into widespread use during the 1950s.
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5,055
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A few years before his death in 1736 Polish-German-Dutch physicist Daniel Gabriel Fahrenheit reportedly constructed a solar microscope, which basically was a combination of the compound microscope with camera obscura projection. It needed bright sunlight as a light source to project a clear magnified image of transparent objects. Fahrenheit's instrument may have been seen by German physician Johann Nathanael Lieberkühn who introduced the instrument in England, where optician John Cuff improved it with a stationary optical tube and an adjustable mirror. In 1774 English instrument maker Benjamin Martin introduced his "Opake Solar Microscope" for the enlarged projection of opaque objects. He claimed:
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5,056
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The solar microscope, was employed in experiments with photosensitive silver nitrate by Thomas Wedgwood in collaboration with Humphry Davy in making the first, but impermanent, photographic enlargements. Their discoveries, regarded as the earliest deliberate and successful form of photography, were published in June 1802 by Davy in his An Account of a Method of Copying Paintings upon Glass, and of Making Profiles, by the Agency of Light upon Nitrate of Silver. Invented by T. Wedgwood, Esq. With Observations by H. Davy in the first issue of the Journals of the Royal Institution of Great Britain.
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5,057
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Swiss mathematician, physicist, astronomer, logician and engineer Leonhard Euler demonstrated an opaque projector, now commonly known as an episcope, around 1756. It could project a clear image of opaque images and objects.
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5,058
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French scientist Jacques Charles is thought to have invented the similar "megascope" in 1780. He used it for his lectures. Around 1872 Henry Morton used an opaque projector in demonstrations for huge audiences, for example in the Philadelphia Opera House which could seat 3500 people. His machine did not use a condenser or reflector, but used an oxyhydrogen lamp close to the object in order to project huge clear images.
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5,059
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See main article: Solar camera
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5,060
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Known equally, though later, as a solar enlarger, the solar camera is a photographic application of the solar microscope and an ancestor of the darkroom enlarger, and was used, mostly by portrait photographers and as an aid to portrait artists, in the mid-to-late 19th century to make photographic enlargements from negatives using the Sun as a light source powerful enough to expose the then available low-sensitivity photographic materials. It was superseded in the 1880s when other light sources, including the incandescent bulb, were developed for the darkroom enlarger and materials became ever more photo-sensitive.
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5,061
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In the early and middle parts of the 20th century, low-cost opaque projectors were produced and marketed as a toy for children. The light source in early opaque projectors was often limelight, with incandescent light bulbs and halogen lamps taking over later. Episcopes are still marketed as artists’ enlargement tools to allow images to be traced on surfaces such as prepared canvas.
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5,062
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In the late 1950s and early 1960s, overhead projectors began to be widely used in schools and businesses. The first overhead projector was used for police identification work. It used a celluloid roll over a 9-inch stage allowing facial characteristics to be rolled across the stage. The United States military in 1940 was the first to use it in quantity for training.
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5,063
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From the 1950s to the 1990s slide projectors for 35 mm photographic positive film slides were common for presentations and as a form of entertainment; family members and friends would occasionally gather to view slideshows, typically of vacation travels.
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5,064
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Complex Multi-image shows of the 1970s to 1990s, purposed usually for marketing, promotion or community service or artistic displays, used 35mm and 46mm transparency slides projected by single or multiple slide projectors onto one or more screens in synchronization with an audio voice-over and/or music track controlled by a pulsed-signal tape or cassette. Multi-image productions are also known as multi-image slide presentations, slide shows and diaporamas and are a specific form of multimedia or audio-visual production.
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5,065
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Digital cameras had become commercialised by 1990, and in 1997 Microsoft PowerPoint was updated to include image files, accelerating the transition from 35 mm slides to digital images, and thus digital projectors, in pedagogy and training. Production of all Kodak Carousel slide projectors ceased in 2004, and in 2009 manufacture and processing of Kodachrome film was discontinued.
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5,066
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In Mad Men's first series the final episode presents the protagonist Don Draper's presentation of a plan to market the Kodak slide carrier a 'carousel'.
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5,067
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A PC speaker is a loudspeaker built into some IBM PC compatible computers. The first IBM Personal Computer, model 5150, employed a standard 2.25 inch magnetic driven speaker. More recent computers use a tiny moving-iron or piezo speaker instead. The speaker allows software and firmware to provide auditory feedback to a user, such as to report a hardware fault. A PC speaker generates waveforms using the programmable interval timer, an Intel 8253 or 8254 chip.
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5,068
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The PC speaker is used during the power-on self-test sequence to indicate errors during the boot process. Since it is active before the graphics card, it can be used to communicate "beep codes" related to problems that prevent the much more complex initialization of the graphics card to take place. For example, the Video BIOS usually cannot activate a graphics card unless working RAM is present in the system while beeping the speaker is possible with just ROM and the CPU registers. Usually, different error codes will be signalled by specific beeping patterns, such as e.g. "one beep; pause; three beeps; pause; repeat". These patterns are specific to the BIOS/UEFI manufacturer and are usually documented in the technical manual of the motherboard.
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5,069
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Several programs, including music software, operating systems or games, could play pulse-code modulation sound through the PC speaker using special Pulse-width Modulation techniques explained later in this article.
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5,070
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The PC speaker was often used in very innovative ways to create the impression of polyphonic music or sound effects within computer games of its era, such as the LucasArts series of adventure games from the mid-1980s, using swift arpeggios. Several games such as Space Hulk and Pinball Fantasies were noted for their elaborate sound effects; Space Hulk, in particular, even had full speech.
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5,071
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However, because the method used to reproduce PCM was very sensitive to timing issues, these effects either caused noticeable sluggishness on slower PCs or sometimes failed on faster PCs . Also, it was difficult for programs to do much else, even update the display, during the playing of such sounds. Thus, when sound cards became mainstream in the PC market after 1990, they quickly replaced the PC speaker as the preferred output device for sound effects. Most newly-released PC games stopped supporting the speaker during the second half of the 1990s.
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5,072
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Several programs, including MP , Scream Tracker, Fast Tracker, Impulse Tracker, and even device drivers for Linux and Microsoft Windows, could play PCM sound through the PC speaker.
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5,073
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Modern Microsoft Windows systems have PC speaker support as a separate device with special capabilities – that is, it cannot be configured as a normal audio output device. Some software uses this special sound channel to produce sounds. For example, Skype can use it as a reserve calling signal device for the case where the primary audio output device cannot be heard .
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5,074
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In the 1990s, a computer virus for Microsoft DOS named "Techno" appeared, playing a melody through the PC speaker while printing the word "TECHNO" on the screen until filled.
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5,075
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In some applications, the PC speaker is affixed directly to the computer's motherboard; in others, including the first IBM Personal Computer, the speaker is attached by wire to a connector on the motherboard. Some PC cases come with a PC speaker preinstalled. A wired PC speaker connector may have a two-, three-, or four-pin configuration, and either two or three wires. The female connector of the speaker connects to pin headers on the motherboard, which are sometimes labeled SPEAKER or SPKR.
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5,076
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The PC speaker is normally meant to reproduce a square wave via only 2 levels of output , driven by channel 2 of the Intel 8253 or 8254 Programmable Interval Timer operating in mode three . The speaker hardware itself is directly accessible via PC I/O port 61H via bit 1 and can be physically manipulated for 2 levels of output . However, by carefully timing a short pulse , and by relying on the speaker's physical filtering properties , it is possible to drive the speaker to various intermediate output levels, functioning as a crude digital-to-analog converter. This technique is called pulse-width modulation and allows approximate playback of PCM audio.
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5,077
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With the PC speaker this method achieves limited quality playback, but a commercial solution named RealSound used it to provide improved sound on several games.
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5,078
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Obtaining a high fidelity sound output using this technique requires a switching frequency much higher than the audio frequencies meant to be reproduced , and the output voltage to be bipolar, in order to make better use of the output devices' dynamic range and power. On the PC speaker, however, the output voltage is either zero or at a Transistor-Transistor Logic level .
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5,079
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The quality depends on a trade-off between the PWM carrier frequency and the number of output levels . The clock rate of the PC's programmable interval timer which drives the speaker is fixed at 1,193,180 Hz, and the product of the audio sample rate times the maximum DAC value must equal this.
Typically, a 6-bit DAC with a maximum value of 63 is used at a sample rate of 18,939.4 Hz, producing poor but recognizable audio.
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5,080
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The audio fidelity of this technique is further decreased by the lack of a properly sized dynamic loudspeaker, specially in modern machines and particularly laptops that use a tiny moving-iron speaker . The reason for this is that PWM-produced audio requires a low-pass filter before the final output in order to suppress switching noise and high harmonics. A normal dynamic loudspeaker does this naturally, but the tiny metal diaphragm of the moving-iron speaker will let much switching noise pass, as will many direct couplings .
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5,081
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This use of the PC speaker for complex audio output became less common with the introduction of Sound Blaster and other sound cards.
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5,082
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The display in modern monitors is typically an LCD with LED backlight, having by the 2010s replaced CCFL backlit LCDs. Before the mid-2000s, most monitors used a cathode-ray tube as the image output technology. A monitor is typically connected to its host computer via DisplayPort, HDMI, USB-C, DVI, or VGA. Monitors sometimes use other proprietary connectors and signals to connect to a computer, which is less common.
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5,083
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Originally, computer monitors were used for data processing while television sets were used for video. From the 1980s onward, computers have been used for both data processing and video, while televisions have implemented some computer functionality. In the 2000s, the typical display aspect ratio of both televisions and computer monitors changed from 4:3 to 16:9.
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5,084
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Modern computer monitors are often functionally interchangeable with television sets and vice versa. As most computer monitors do not include integrated speakers, TV tuners, or remote controls, external components such as a DTA box may be needed to use a computer monitor as a TV set.
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5,085
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Early electronic computer front panels were fitted with an array of light bulbs where the state of each particular bulb would indicate the on/off state of a particular register bit inside the computer. This allowed the engineers operating the computer to monitor the internal state of the machine, so this panel of lights came to be known as the 'monitor'. As early monitors were only capable of displaying a very limited amount of information and were very transient, they were rarely considered for program output. Instead, a line printer was the primary output device, while the monitor was limited to keeping track of the program's operation.
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5,086
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One of the first uses of a standalone computer monitor with a personal computer was with the Apple 1, which connected directly to a consumer television as a monitor instead of using a glass terminal as its output.
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Computer monitors were formerly known as visual display units , particularly in British English. This term mostly fell out of use by the 1990s.
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Multiple technologies have been used for computer monitors. Until the 21st century most used cathode-ray tubes but they have largely been superseded by LCD monitors.
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The first computer monitors used cathode-ray tubes . Prior to the advent of home computers in the late 1970s, it was common for a video display terminal using a CRT to be physically integrated with a keyboard and other components of the workstation in a single large chassis, typically limiting them to emulation of a paper teletypewriter, thus the early epithet of 'glass TTY'. The display was monochromatic and far less sharp and detailed than on a modern monitor, necessitating the use of relatively large text and severely limiting the amount of information that could be displayed at one time. High-resolution CRT displays were developed for specialized military, industrial and scientific applications but they were far too costly for general use; wider commercial use became possible after the release of a slow, but affordable Tektronix 4010 terminal in 1972.
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Some of the earliest home computers were limited to monochrome CRT displays, but color display capability was already a possible feature for a few MOS 6500 series-based machines , and the color output was a specialty of the more graphically sophisticated Atari 800 computer, introduced in 1979. Either computer could be connected to the antenna terminals of an ordinary color TV set or used with a purpose-made CRT color monitor for optimum resolution and color quality. Lagging several years behind, in 1981 IBM introduced the Color Graphics Adapter, which could display four colors with a resolution of 320 × 200 pixels, or it could produce 640 × 200 pixels with two colors. In 1984 IBM introduced the Enhanced Graphics Adapter which was capable of producing 16 colors and had a resolution of 640 × 350.
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By the end of the 1980s color progressive scan CRT monitors were widely available and increasingly affordable, while the sharpest prosumer monitors could clearly display high-definition video, against the backdrop of efforts at HDTV standardization from the 1970s to the 1980s failing continuously, leaving consumer SDTVs to stagnate increasingly far behind the capabilities of computer CRT monitors well into the 2000s. During the following decade, maximum display resolutions gradually increased and prices continued to fall as CRT technology remained dominant in the PC monitor market into the new millennium, partly because it remained cheaper to produce. CRTs still offer color, grayscale, motion, and latency advantages over today's LCDs, but improvements to the latter have made them much less obvious. The dynamic range of early LCD panels was very poor, and although text and other motionless graphics were sharper than on a CRT, an LCD characteristic known as pixel lag caused moving graphics to appear noticeably smeared and blurry.
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There are multiple technologies that have been used to implement liquid-crystal displays . Throughout the 1990s, the primary use of LCD technology as computer monitors was in laptops where the lower power consumption, lighter weight, and smaller physical size of LCDs justified the higher price versus a CRT. Commonly, the same laptop would be offered with an assortment of display options at increasing price points: monochrome, passive color, or active matrix color . As volume and manufacturing capability have improved, the monochrome and passive color technologies were dropped from most product lines.
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TFT-LCD is a variant of LCD which is now the dominant technology used for computer monitors.
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The first standalone LCDs appeared in the mid-1990s selling for high prices. As prices declined they became more popular, and by 1997 were competing with CRT monitors. Among the first desktop LCD computer monitors were the Eizo FlexScan L66 in the mid-1990s, the SGI 1600SW, Apple Studio Display and the ViewSonic VP140 in 1998. In 2003, LCDs outsold CRTs for the first time, becoming the primary technology used for computer monitors. The physical advantages of LCD over CRT monitors are that LCDs are lighter, smaller, and consume less power. In terms of performance, LCDs produce less or no flicker, reducing eyestrain, sharper image at native resolution, and better checkerboard contrast. On the other hand, CRT monitors have superior blacks, viewing angles, and response time, can use arbitrary lower resolutions without aliasing, and flicker can be reduced with higher refresh rates, though this flicker can also be used to reduce motion blur compared to less flickery displays such as most LCDs. Many specialized fields such as vision science remain dependent on CRTs, the best LCD monitors having achieved moderate temporal accuracy, and so can be used only if their poor spatial accuracy is unimportant.
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High dynamic range has been implemented into high-end LCD monitors to improve grayscale accuracy. Since around the late 2000s, widescreen LCD monitors have become popular, in part due to television series, motion pictures and video games transitioning to widescreen, which makes squarer monitors unsuited to display them correctly.
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Organic light-emitting diode monitors provide most of the benefits of both LCD and CRT monitors with few of their drawbacks, though much like plasma panels or very early CRTs they suffer from burn-in, and remain very expensive.
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The performance of a monitor is measured by the following parameters:
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On two-dimensional display devices such as computer monitors the display size or viewable image size is the actual amount of screen space that is available to display a picture, video or working space, without obstruction from the bezel or other aspects of the unit's design. The main measurements for display devices are width, height, total area and the diagonal.
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The size of a display is usually given by manufacturers diagonally, i.e. as the distance between two opposite screen corners. This method of measurement is inherited from the method used for the first generation of CRT television when picture tubes with circular faces were in common use. Being circular, it was the external diameter of the glass envelope that described their size. Since these circular tubes were used to display rectangular images, the diagonal measurement of the rectangular image was smaller than the diameter of the tube's face . This method continued even when cathode-ray tubes were manufactured as rounded rectangles; it had the advantage of being a single number specifying the size and was not confusing when the aspect ratio was universally 4:3.
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With the introduction of flat panel technology, the diagonal measurement became the actual diagonal of the visible display. This meant that an eighteen-inch LCD had a larger viewable area than an eighteen-inch cathode-ray tube.
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