what is monitor

what is monitor

It is the most commonly used display device. The monitor utilizes a cathode ray tube (CRT). CRT monitors generally produce images by the raster-scan method. In this method, an electron beam varying in intensity is moved back and forth horizontally across the face of the monitor. As the beam is directed to each spot on the phosphor-coated screen, it illuminates the spot in proportion to the voltage applied to the beam. Each spot represents a picture element or pixel. When the electron beam has scanned the entire screens and illuminated each pixel. One can see a complete image. The image that can be seen is the one traced on the retinas of eyes by the light beam. However, this image will fade unless it is refreshed. Thus, the electron beam must scan the screen very rapidly (a minimum of 60 times per second), so that the intensity of the image remains approximately the same and the screen docs not appear to flicker.

The number of pixels that make up the screen determines the screen resolution of a particular monitor. Monitors are currently available with 64,000 to more than 2 million pixels per screen. The greater the resolution of a monitor the greater the storage demand on the computer. This is because the image must he stored in memory before it can he displayed. Two techniques used to store computer images are bit-mapped and character-addressable. In a bit-mapped display, each pixel is uniquely addressable. Information must be stored for each pixel on the screen. This technique needs quite a large computer memory and provides the most detailed display. For graphical applications, such as CAD/CAM, this detail is essential. However, for applications such as word processing, addressable display is appropriate. In a character addressable display, the screen is divided into chaacter positions. Only the characters to be displayed are stored in memory. As each character is retrieved from memory, it is converted into a pattern of dots or pixels by a special character generator module.

Monochrome or Color

Some monitors display images in only one color, while others are capable of producing images in colors. Monochrome monitors use a single electron beam and display one color, generally green, amber, or white, on a black background. The phosphor composition of the screen determines the color. Color monitors produce multi-color images by combining the red, blue and green colors in varying intensities. Each pixel is made up of three-color dots: red, blue, and green. It will appear to glow in different colors depending on the intensity of each individual dot in the pixel. Color monitors are commonly referred to as RGB monitors since they employ three election beams, one of each color. Color monitors are categorized as CGA, EGA, VGA and SVGA depending on the resolution. CGA monitors provide the least resolution (approximately 300 * 200 Pixels) and SVGA monitors provide the greatest resolution (1000 * 800 pixels and greater) resolution.

Monitor Interface

A monitor requires an appropriate interface to communicate with a computer. For example, a color graphics interface board is needed for a color monitor. This interface will generally not work with a monochrome monitor and might even damage it. Dozens of monitor interface boards are available for use with microcomputers. A caution must be exercised to match the interface to both the monitor and the computer.

Using a Television

Some smaller microcomputer systems can be used with a standard television. The basic difference between a monitor and a television set is that the resolution of a television is substantially less than that with a monitor. Also the television requires the use of a modulator to interface the computer output with the television. The modulator combines the separate audio and visual signals sent by the microcomputer into a single modulated signal as required by a television. Most inexpensive computer systems designed for use with a television set generally have a built-in modulator with a standard television. The basic difference between a monitor and television set is that the resolution of a television is substantially less as television set generally have a built-in modulator.

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