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Output Devices This are monitors, sound and video cards, and printers. Monitors The primary component in every monitor is the Cathode Ray Tube. (CRT) The CRT displays all the images that you see in the monitor through the use of Picture Elements, or pixels. A pixel is a single dot on the screen that can be one of three colors; red, blue, or green. All of the above elements work together to produce images on the screen. An electron beam moves from top to bottom and left to right one row at a time. When the electron beam hits a pixel, it illuminates that pixel in the appropriate color for an incredibly short period of time. By combining the different pixels in different colors, the monitor can produce any image, much the same way a TV works. Refresh Rate When the electron beam scans across a pixel, it illuminates that pixel for a very short period of time. Therefore, the electron beam must scan that pixel multiple times a second in order to maintain the image on the screen. The refresh rate is the time it takes for the CRT's electron beam to scan across the entire screen from top to bottom, measured in hertz (Hz). Remember that SVGA monitors must maintain a 70Hz refresh rate to meet the VESA organization's minimum standards for SVGA. Interlacing Most current monitors are non-interlaced, You will need to know what interlacing means. Non-interlaced monitors scan the entire CRT in one pass, where interlaced monitors must make two passes. Interlaced monitors only scan the odd pixels first, then the even pixels. Interlaced monitors are cheaper to produce, but they flicker more and are less desirable. With the reduction in costs in monitor technology, pretty much every monitor you find will be non-interlaced. Resolution The number of pixels in a monitor determine the picture quality that monitor can produce, referred to as it's resolution. Resolution is stated in a width times height number, such as 640x480. 640 represents 640 pixels wide across the monitor, and the 480 means their are 480 rows of pixels. Monitors use two different technologies to produce images. The first is called a Shadow Mask, which is a metal screen that separates each pixel from the pixel next to it. Essentially, the shadow mask is a piece of metal with thousands of little holes that line up with each pixel on the screen. The mask absorbs any stray electrons from illuminating the pixel next to the desired pixel. This keeps the monitor from blurring, but produces a black border around each pixel. The other technology is called an Aperture Grill. The aperture grill uses vertical wires to keep stray electrons from creeping into other pixels, and lets the spacing between pixels to be decreased. Horizontal wires hold the vertical wires in place to ensure that the vertical wires don't move or vibrate. Dot Pitch Dot pitch is the distance between pixels, no matter which technology is used. An aperture grill has a lower dot pitch, because the spacing in pixels is reduced by the use of wires. The smaller the dot pitch, the better the picture quality. Dot pitch is measured in millimeters, like .25 and .21. Having a smaller dot pitch also allows more pixels to be used, which improves the resolution. Monitor Safety and the Environment Essentially, you should NEVER open a monitor's case, because there are very few serviceable parts inside a monitor. More importantly, the monitor can kill you fairly easily, and contains over 20,000 volts of power or more even when it's turned off. You probably will see a question regarding ESD wrist straps that deals with monitors. You NEVER wear an ESD strap while working inside a monitor. With the power that a monitor holds, wearing an ESD strap makes you the shortest path for the electrical power in a monitor to travel. Make sure the plug is out of the outlet, and don't ever open a case unless you have to. One tool you can use to try to fix monitor troubles is called degaussing. As electrical circuits are used, they slowly build up a magnetic charge. As more magnetic charge is created, the images on the screen will slowly blur. The degaussing tool is normally built in to most current monitors. You also should be aware that speakers produce large magnetic field which can interfere with monitor operations. Make sure you use magnetically shielded speakers, or place your speakers away from the monitor. Only clean monitors when they're powered down, as you can cause harm to yourself and the monitor by cleaning a monitor with a liquid while it still is powered on. The Environmental Protection Agency (EPA) mandates several features that must be present on monitors sold in the United States. These are called the Energy Star guidelines, and mandate that monitors use less than 30 Watts of power in all modes. In sleep modes, the monitor must use only 1% of the power it would use in active mode. Video Cards Over the years there have been several different video cards standards. The original video cards where monochrome (black and white), and were labeled Monochrome Display Adaptors. (MDA) Some servers and text-based operating system computers still use MDA, as resolution is not an issue and they don't require graphics. Color Graphics Adapters (CGA) were the first color video cards. They were capable of 320x200 using four colors or 640x200 using two colors. Enhanced Graphics Adapters (EGA) supported 16 colors at up to 640x350 resolution. CGA and EGA are not used on any current computers. Video Graphics Array (VGA), Super Video Graphics Array (SVGA), and Ultra Video Graphics Array (UVGA) are video adapters that support a minimum of 640x480 at 16 colors. SVGA and UVGA both support resolutions as high as 1600x1200 and have up to 16 million colors available for use. Video Processors and Video Ram The original video adapters used the main board processor to process their images, and were merely a device to transfer the images to the monitor. More recently, video processors have become more complex, having their own multiple processors and video RAM built on to the adapter card. This allows the CPU to issue commands for the video card to process rather than doing the processing itself, freeing up CPU time. There are many different kinds of Video RAM. Some of this RAM is the same RAM used by the motherboard and some use exotic RAM technology only used on Video Cards. Here are some old and current video RAM types and their descriptions;
Some video cards are integrated into the main board. Manufactures do this to reduce costs and make their motherboards easier to install. Unfortunately, this means that the video card uses normal main board memory, and they are invariably slower than expansion video cards. Figuring Out What Video Card Memories Mean You will probably see about video card memory sizes and you should know how to calculate video card memory sizes. Like "You have an image that requires 800x600 resolution with 16-bit color. How much video RAM do you require?" Here is how to figure this size out;
The answer is 960K of video RAM, and therefore at least 1MB of video memory. Video Card Connections There are two connections that you must make with a video card; The monitor connection and the bus connection. Monitor connections on everything but specialized monitors is always done through a 15-pin D-connector, although CGA and MDA used to use the 9-pin format. Some specialized monitors use BNC barrel connectors, but you probably won't see any monitors of this type any more. The other connection is to the motherboard itself. Most current video cards use the Advanced Graphics Port (AGP), but previous video cards could use the Peripheral Component Interface (PCI), VESA-Local Bus (VLB), and Industry Standard Architecture (ISA) expansion ports. Sound Cards The last section in this week's tutorial is on sound cards. Sound cards have evolved over the past few years, but not at the same rate as video cards. There are two sound card standards; SoundBlaster (Named after the first available sound cards) and General MIDI. (Musical Instrument Digital Interface) Most sound cards are compatible with both formats. Most sound cards are CD-Quality, meaning they reproduce and capture sounds at a quality equal to a Compact Disk. CD-ROM drives connect to sound cards, allowing them to play CD's through the sound card. An Audio cable connects the CD-ROM drive to the sound card. The standard settings and connectors are;
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