No. 14 Monitors

 

What is a Monitor?

The monitor, also called the video display terminal (VDT), is the part of the personal computer system that looks like a TV screen. It allows the user to see text and graphics as it is entered into the computer. Making the text and graphics visible is actually the job of the display adapter, which usually takes the form of an enhancement board that snaps into one of the expansion slots inside the central processing unit (CPU). The display adapter and monitor work together to translate the applications and data into something the monitor can use and we can see.

 

Until recently, monitors that displayed in color were not considered essential for serious computing. All that is changing as computer working environments rely more on graphics.

First, some basic vocabulary:

 

Pixel -- One element of a video display's resolution, or one dot on the screen. Characters and symbols are composed of many pixels. The number of possible pixels that can be displayed is referred to as the resolution of the screen: the greater the number of pixels, the higher the resolution.

 

Resolution -- A measurement, usually expressed in linear dots per inch (dpi), of the sharpness of an image generated by an output device such as a printer or monitor.

 

Bit map -- The representation of a video image stored in the computer's memory. Each pixel is controlled by an on or off code stored as a bit in the computer's memory. Bit- mapped images consume large amounts of memory.

 

What is a monochrome monitor?

A monochrome monitor is a video display on which one primary color is available, usually white, with one background color, usually black. A monochrome display adapter (MDA) is a single-color display adapter for IBM computers that displays text, but not graphics with a resolution of 720 pixels horizontally and 350 lines vertically. An example of an MDA is the Hercules Graphics Adapter. It works only with graphics software that includes drivers for its non-IBM display format. For example, software designed to work with CGA (explained below) does not display graphics on systems equipped with the Hercules cards UNLESS the software specifically includes a Hercules driver. Many shareware and lower prices graphics programs do not include the necessary driver and will not work. Hercules display adapters work with all programs that display monochrome text.

 

What is CGA?

A Color Graphics Adapter is a low to medium-resolution color graphic system for personal computers. It is a bit-mapped adapter that displays either four colors simultaneously with a resolution of 200 pixels horizontally and 320 lines vertically or ONE color with a resolution of 620 pixels horizontally and 200 lines vertically. CGA monitors were the first to appear for DOS-based computers. A monochrome composite is a type of video display that attaches to a CGA. It does not provide color, but some models support "color" in the form of shading.

 

What is a digital monitor?

This is a cathode ray tube (CRT) display that accepts digital output from the display adapter and converts the digital signal to an analog one. The CRT is an electronic vacuum tube containing a screen on which information is displayed. Most common monitors and all standard TV sets use CRTs. Digital monitors cannot accept input unless it conforms to a standard such as MDA or CGA (see above) or enhanced graphics adapter (EGA). EGA is a medium-resolution color system for personal computers. It is a bit-mapped adapter for IBMs and compatibles that displays up to 16 colors simultaneously with a resolution of 640 pixels horizontally and 350 lines vertically. Digital monitors are fast and produce sharp images; however, they do not display continuously variable colors. They display in only two modes: on or off. This makes it difficult to see subtle distinctions in color.

 

A composite color monitor accepts a standard video analog signal that mixes RED, GREEN, and BLUE signals to produce the color image. It does not provide high resolution. An RGB (Red Green Blue) monitor accepts separate inputs for each color and produces a sharper image. Although the enhanced graphics display uses RGB techniques, the RGB monitor is the same as the CGA standard.

 

What is an analog monitor?

This monitor accepts a continuously varied video signal and thus displays a continuous range of colors. VGAs -- Video Graphics Arrays -- are analog. VGA monitors display as many as 256 colors simultaneously, with a resolution of 640 pixels horizontally and 480 lines vertically. VGA circuitry is compatible with all previous IBM display standards. VGA uses an analog signal that converts digital information into different voltage levels that vary the brightness of a pixel. The process requires less memory than EGA and is more versatile. Super VGA has a resolution of 800 pixels by 600 lines; even more advanced adapters have a resolution of 1,024 pixels by 768 lines. A multisync monitor is capable of adjusting to a range of input frequencies so that it can work with a variety of display adapters -- the higher the frequency, the greater the on-screen resolution.

 

VGA monitors, unlike EGA ones, preserve the aspect ratio of on-screen graphic images. The aspect ratio is the ratio of the horizontal dimension to the vertical dimension. Unless the correct width to height ratio is maintained, the image will appear distorted.

 

Do I need an analog monitor?

Probably yes. Much of today's software, including Windows, may support EGA monitors, but Super-VGA is now considered the entry-level display technology for using Windows well. Usually VGA costs only slightly more than EGA and is worth the price.

 

What about the monitors on laptop computers?

There are basically two types of displays for laptop computers. A liquid crystal display (LCD) is a low-power display technology that uses rod-shaped crystal molecules that change their orientation when an electrical current flows through them. LCD displays are flat and draw little power but they are not very bright. This can cause eyestrain after prolonged use. Some LCD monitors use a backlit screen that improves the brightness but also draws more power. A plasma display is used with more expensive laptops. The display is produced by energizing an ionized gas held between to transparent panels.

 

Apple Computers

The above standards are for IBMs and compatibles. Apple Macintosh's have always led the way in color graphics. Those with nine inch screens display 512 pixels by 342 lines; those with 12 or 13 inch monitors display 640 pixels by 480 lines.