{"id":291,"date":"2020-08-18T19:23:47","date_gmt":"2020-08-18T20:23:47","guid":{"rendered":"http:\/\/www.linux-tutorial.info\/?page_id=77"},"modified":"2020-08-22T19:26:41","modified_gmt":"2020-08-22T20:26:41","slug":"this-is-the-page-title-toplevel-126","status":"publish","type":"page","link":"http:\/\/www.linux-tutorial.info\/?page_id=291","title":{"rendered":"Video Cards and Monitors"},"content":{"rendered":"\nVideo Cards and Monitors<\/title>\n<p>\nWithout a video card and monitor,\nyou don’t see anything. In fact, every PC that I have ever seen won’t even\n<glossary>boot<\/glossary> unless there is a video card in it. Granted, your\ncomputer could boot and even work without being attached to a monitor (and I\nhave seen those), but it’s no fun unless you get to see whats going on.\n<\/p>\n<p>\nWhen PCs first hit the market, there was only one kind of video system. High\nresolution and millions of colors were something you read about in\nscience-fiction novels. Times changed and so did graphics adapters. The first\ndramatic change was with the introduction of color with IBM’s color graphics\nadapter (CGA), which required a completely new (and incompatible) video\nsubsystem. In an attempt to integrate color and monochrome systems, IBM came out\nwith the enhanced graphics adapter (EGA).\n<\/p>\n<p>\nBut I’m not going to talk about\nthose. Why? First, no one buys them anymore. I doubt that anyone still makes\nthem. If you could find one, there would be no problem at all to install them\nand get them to work. The second reason why I am not going to talk about them is\nbecause they are not that common. Because “no one” uses them any more, the time\nI spend telling you why I won’t tell you about them is already too much.\n<\/p>\n<p>\nWhat are we going to talk about instead? Well, the first thing is Video\nGraphics Array (VGA). <glossary>VGA<\/glossary> is the standard by which\nvirtually all video card manufacturers base their products. Though enhancements\nto VGA (Super VGA or SVGA) exists, it is all based on VGA.\n<\/p>\n<p>\nWhen talking\nabout <glossary>VGA<\/glossary>, I first need to talk about some basics of video\ntechnology. The first issue is just how things work. Digital signals are sent\nby the <glossary>operating system<\/glossary> to the video card, which sends them\nthrough a digital-to-analog converter (DAC). Usually a single chip contains\nthree DACs, one for each color (red, green, and blue, or RGB). The\n<glossary>DAC<\/glossary> has a look-up table that determines the voltage to be\noutput on each line for the respective color.\n<\/p>\n<p>\nThe voltage that the\n<glossary>DAC<\/glossary> has found for a given color is sent to the three\nelectron guns at the back of the monitors cathode ray tube (CRT), again, one\nfor each color. The intensity of the electron stream is a result of this\nvoltage.\n<\/p>\n<p>\nThe video adapter also sends a <glossary>signal<\/glossary> to\nthe<em> magnetic deflection yoke<i>,<\/i><\/em> which aims the electron beams to\nthe right place on the screen. This signal determines how far apart the dots\nare, as well as how often the screen is redrawn. The dots are referred to as\n<em>pixels<\/em>, the distance apart they are is the <em>pitch<i>,<\/i> <\/em>and\nhow often the screen is redrawn is the <em>refresh rate.\n<\/p><\/em>\n<p>\nTo keep the\nbeams precisely aligned, they first pass through a <em>shadow mask<\/em>, a metal\nplate containing hundreds of thousands of little holes. The dot pitch is distance\nbetween the holes in the shadow mask. The closer the holes, the lower the pitch. A\nlower pitch means a sharper image.\n<\/p>\n<p>\nThe electrons from the electron guns\nstrike the phosphors inside the monitor screen and make them glow. Three\ndifferent phosphors are used, one for each color. The stronger the beams, the\nmore intense the color. Colors other than RGB are created by varying the amount\ndisplayed each of these three colors, that is, changing the intensity of each\ncolor. For example, purple would be created by exciting red and blue but no\ngreen phosphors. After the beams stops hitting the phosphor, it still continues\nto glow for a short time. To keep the image on the screen, the phosphor must be\nrecharged by the electron beam again.\n<\/p>\n<p>\nThe electron beams are moved across\nthe screen by changing the deflection yoke. When the beams reach the other side,\nthey are turned off and returned to the starting side, just below the line where\nthey left off. When the guns reach the last line, they move back up to the top.\nThis is called <em>raster scanning<\/em> and it is done approximately 60 times a\nsecond.\n<\/p>\n<p>\nWhen the beam has completed a line, it needs to return to the\nother end to begin the new line. This is called <i>horizontal<\/i>\n<i>retrace.<\/i> Similarly, when the beam has reached the bottom, it needs to\nmove back to the top again. This is the <i>vertical retrace.<\/i> In both cases,\nthe beams intensity is reduced to the point that nothing <\/glossary>is drawn on\nthe screen. (This is called <i>blanking.)<\/p><\/i>\n<p>\nSome monitor manufacturers\ntry to save money by using less expensive components. The trade off is that the\nbeams cannot scan every line during each pass. Instead, they scan every other\nline during the first pass then scan the lines they missed during the second\npass. This is called interlacing because the scan lines are <em>interlaced<\/em>.\nAlthough this provides higher resolutions in less expensive monitors, the images\nwill “flicker” because the phosphors begin to fade before they can be recharged.\n(This flickering gives me, and other people, a headache.)<\/p>\n<p>\nFor most users,\nthe most important aspect is the <em>resolution<\/em>. Resolution determines the\ntotal number of pixels that can be shown on the screen. In graphics mode,\nstandard <glossary>VGA<\/glossary> has a resolution of 640 pixels horizontally\nand 480 pixels vertically. By convention, you say that your resolution is\n640-by-480.\n<\/p>\n<p>\nA pixel is actually a set of three phosphors rather than just\na single phosphor. So, in essence, a pixel is a single spot of color on the\nscreen. What color is shown at any given location is an <em>interaction<\/em>\nbetween the <glossary>operating system<\/glossary> and the video card. Years ago,\nthe operating system (or program) had to tell the video card where each dot on\nthe screen was. It had an internal array (or table) of pixels, each containing\nthe appropriate color values. Today, some video cards can be told to\n<em>draw<\/em>. They don’t need to know that there is a row of red dots between\npoints A and B. Instead, they are simply told to draw a red line from point A to\npoint B. This results in faster graphics because the video card has taken over\nmuch of the work.\n<\/p>\n<p>\nIn other cases, the system still needs to keep track of\nwhich colors are where. If we had a truly monochrome video system, any given\npixel would either be on or off. Therefore, a single bit can be used to store\nthat information. If we go up to 16 colors, we need 4 bits, or half a byte of\ninformation (2<sup>4 <\/sup>= 16). If we go to a whole byte, then we can have 256\ncolors at once (2<sup>8<\/sup>). Many video cards use three bytes to store the\ncolor data, one for each of the primary colors (RGB). In this way, they can get\nmore than 16 million colors!\n<\/p>\n<p>\nNow, 16 million colors seems like a lot,\nand it is. However, it’s actually too much. Humans cannot distinguish that many\ncolors, so much of the ability is wasted. Add to that that most monitors are\nlimited to just a few hundred thousand colors. So, no matter what your friends\ntell you about how wonderful their video card is that does 16 million colors,\nyou need not be impressed. The odds are the monitor can’t handle them and you\ncertainly can’t see them.\n<\/p>\n<p>\nHowever, don’t think that the makings of video\ncards are trying to rip us off. In fact, it’s easier to design cards that are\nmultiples of whole bytes. If we had a 18-bit display (which is needed to get the\n250K of colors that monitors could handle), we either use 6 bits of three\ndifferent bytes or two whole bytes and 2 bits of the third. Either way, things\nare wasted and you spend time processing the bits. If you know that you have to\nread three whole bytes, one for each color, then there is not as much\nprocessing.\n<\/p>\n<p>\nHow many pixels and how many colors a video card can show\nare interdependent of each other. When you bought it, your video card came with\na certain amount of memory. The amount of memory it has limits the total number\nof pixels and colors you can have. If you take the standard resolution of a\n<glossary>VGA<\/glossary> card of 640×480 pixels, that’s 307,200 pixels. If we\nwant to show 16 colors, that’s 307,200 x 4 bits or 1,228,800 bits. Dividing this\nby eight gives you 153,600 bytes needed to display 640×480 in 16 colors. Because\nmemory is usually produced in powers of two, the next smallest size is 256\nKilobytes. Therefore, a video card with 256K of memory is needed.\n<\/p>\n<p>\nMaybe\nthis is enough. For me, I don’t get enough on the screen with 640×480, and only\n16 colors looks terrible (at least to me). However, if you never run any\ngraphics applications on your machines, such as X-Windows, then there is no need\nfor anything better. Operating in <em>text mode<i>,<\/i><\/em> your video card\ndoes fine.\n<\/p>\n<p>\nAs I said, I am not happy with this. I want more. If I want to\ngo up to the next highest resolution (800×600) with 16 colors, I need 240,000\nbytes. I still have less than the 256K I need for 640×480 and 16 colors. If,\ninstead, I want 256 colors (which requires 8 bits per pixel), I need at least\n480,000. I now need 512K on the video card.\n<\/p>\n<p>\nNow I buy a great big\nmonitor and want something closer to “true color.” Lets not get greedy, but say\nI wanted a resolution of 1,024×768 (the next highest up) and “only” 65,635\ncolors. I now need 1,572,864 bytes of memory. Because my video card has only 1Mb\nof memory, I’m out of luck!\n<\/p>\n<p>\nBut wait a minute! Doesn’t the\n<glossary>VGA<\/glossary> standard only support resolutions up to 640×480? True.\nHowever, the Video Electronics Standards Association (VESA) has defined\nresolutions more than 640×480 as Super VGA. In addition to the resolutions I\nmentioned previously (800×600 and 1,024×768), <glossary>SVGA<\/glossary> also\nincludes 1,280×1,024 and 1,600×1,200.\n<\/p>\n<p>\nOkay. The mere fact that you have\na video card that handle <glossary>SVGA<\/glossary> resolutions does not mean you\nare going to get a decent picture (or at least not the picture you want). Any\nsystem is only as good as its worst component, and this also applies to your\nvideo system. It is therefore important to understand a characteristic of your\nmonitor: pitch. I mentioned this briefly before, but it is important to talk\nabout it further.\n<\/p>\n<p>\nWhen shopping for a monitor, you will often see that\namong the characteristics used to sell it is the pitch. The values you would see\ncould be something like .39 or .28, which is the spacing between the holes in\nthe shadow <glossary>mask<\/glossary>, measured in millimeters. Therefore, a\npitch of .28 is just more than one-quarter of a millimeter. The lower the pitch,\nthe closer together the holes and the sharper the image. Even if you aren’t\nusing any graphics-oriented programs, it’s worth the few extra dollars to get a\nlower pitch and the resulting sharper image.\n<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Video Cards and Monitors Without a video card and monitor, you don’t see anything. In fact, every PC that I have ever seen won’t even boot unless there is a video card in it. Granted, your computer could boot and … <a href=\"http:\/\/www.linux-tutorial.info\/?page_id=291\">Continue reading <span class=\"meta-nav\">→<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-291","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"http:\/\/www.linux-tutorial.info\/index.php?rest_route=\/wp\/v2\/pages\/291","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/www.linux-tutorial.info\/index.php?rest_route=\/wp\/v2\/pages"}],"about":[{"href":"http:\/\/www.linux-tutorial.info\/index.php?rest_route=\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"http:\/\/www.linux-tutorial.info\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/www.linux-tutorial.info\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=291"}],"version-history":[{"count":1,"href":"http:\/\/www.linux-tutorial.info\/index.php?rest_route=\/wp\/v2\/pages\/291\/revisions"}],"predecessor-version":[{"id":784,"href":"http:\/\/www.linux-tutorial.info\/index.php?rest_route=\/wp\/v2\/pages\/291\/revisions\/784"}],"wp:attachment":[{"href":"http:\/\/www.linux-tutorial.info\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=291"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}