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Computer Monitors


      The computer monitor is an output device that is part of your computer's display system. A cable connects the monitor to a video adapter (video card) that is installed in an expansion slot on your computerís motherboard. This system converts signals into text and pictures and displays them on a TV-like screen (the monitor).

The computer sends a signal to the video adapter, telling it what character, image or graphic to display. The video adapter converts that signal to a set of instructions that tell the display device (monitor) how to draw the image on the screen.

Cathode Ray Tube (CRT)
The CRT, or Cathode Ray Tube, is the "picture tube" of your monitor. Although it is a large vacuum tube, it's shaped more like a bottle. The tube tapers near the back where there's a negatively charged cathode, or "electron gun". The electron gun shoots electrons at the back of the positvely charged screen, which is coated with a phosphorous chemical. This excites the phosphors causing them to glow as individual dots called pixels (picture elements). The image you see on the monitor's screen is made up of thousands of tiny dots (pixels). If you've ever seen a child's LiteBrite toy, then you have a good idea of the concept. The distance between the pixels has a lot to do with the quality of the image. If the distance between pixels on a monitor screen is too great, the picture will appear "fuzzy", or grainy. The closer together the pixels are, the sharper the image on screen. The distance between pixels on a computer monitor screen is called its dot pitch and is measured in millimeters. (see sidebar). You should try to get a monitor with a dot pitch of .28 mm or less.

Note: From an environmental point of view, the monitor is the most difficult computer peripheral to dispose of because of the lead it contains.

inside monitorThere are a couple of electromagnets (yokes) around the collar of the tube that actually bend the beam of electrons. The beam scans (is bent) across the monitor from left to right and top to bottom to create, or draw the image, line by line. The number of times in one second that the electron gun redraws the entire image is called the refresh rate and is measured in Hertz (Hz).
If the scanning beam hits each and every line of pixels, in succession, on each pass, then the monitor is known as a non-interlaced monitor. A non-interlaced monitor is preferred over an interlaced monitor. The electron beam on an interlaced monitor scans the odd numbered lines on one pass, then scans the even lines on the second pass. This results in an almost imperceivable flicker that can cause eye-strain.

interlaced monitor

This type of eye-strain can result in blurred vision, sore eyes, headaches and even nausea. Don't buy an interlaced monitor, they can be a real pain in the ... ask your optometrist.

Interlaced computer monitors are getting harder to find (good!), but they are still out there, so keep that in mind when purchasing a monitor and watch out for that "steal of a deal".

Video Technologies
      Video technologies differ in many different ways. However, the major 2 differences are resolution and the number of colors it can produce at those resolutions.

      Resolution is the number of pixels that are used to draw an image on the screen. If you could count the pixels in one horizontal row across the top of the screen, and the number of pixels in one vertical column down the side, that would properly describe the resolution that the monitor is displaying. Itís given as two numbers. If there were 800 pixels across and 600 pixels down the side, then the resolution would be 800 X 600. Multiply 800 times 600 and youíll get the number of pixels used to draw the image (480,000 pixels in this example). A monitor must be matched with the video card in the system. The monitor has to be capable of displaying the resolutions and colors that the adapter can produce. It works the other way around too. If your monitor is capable of displaying a resolution of 1,024 X 768 but your adapter can only produce 640 X 480, then thatís all youíre going to get.
      When we talk about the different technologies, weíre talking about the video card and monitor that make up that display system. Also, standards describe the basic number of colors and resolutions for each technology, but individual manufacturers always take liberties, providing options and enhancements that are designed to make their product more appealing to the end user. This is, of course, how new standards come about.

      Monochrome monitors are very basic displays that produce only one color. The basic text mode in DOS is 80 characters across and 25 down. When graphics were first introduced, they were fairly rough by todayís standards, and you had to manually type in a command to change from text mode to graphics mode. A company called Hercules Graphics developed a video adapter that could do this for you. Not only could it change from text to graphics, but it could do it on the fly whenever the application required it. Todayís adapters still basically use the same methods.

      The Color Graphics Adapter (CGA) introduced color to the personal computer. In APA mode it can produce a resolution of 320 X 200 and has a palette of 16 colors but can only display 4 at a time. With the introduction of the IBM Enhanced Graphics Adapter (EGA), the proper monitor was capable of a resolution of 640 X 350 pixels and could display 16 colors from a palette of 64.

      Up until VGA, colors were produced digitally. Each electron beam could be either on or off. There were three electron guns, one for each color, red, green and blue (RGB). This combination could produce 8 colors. By cutting the intensity of the beam in half, you could get 8 more colors for a total of 16. IBM came up with the idea of developing an analog display system that could produce 64 different levels of intensity. Their new Video Graphics Array adapter was capable of a resolution of 640 X 480 pixels and could display up to 256 colors from a palette of over 260,000. This technology soon became the standard for almost every video card and monitor being developed.

      Once again, manufacturers began to develop video adapters that added features and enhancements to the VGA standard. Super-VGA is based on VGA standards and describes display systems with several different resolutions and a varied number
of colors. When SVGA first came out it could be defined as having capabilities of 800 X 600 with 256 colors or 1024 X 768 with 16 colors. However, these cards and monitors are now capable of resolutions up to 1280 X 1024 with a palette of more than 16 million colors.

      Extended Graphics Array was developed by IBM. It improved upon the VGA standard (also developed by IBM) but was a proprietary adapter for use in Micro Channel Architecture expansion slots. It had its own coprocessor and bus-mastering ability, which means that it had the ability to execute instructions independent of the CPU. It was also a 32-bit adapter capable of increased data transfer speeds. XGA allowed for better performance, could provide higher resolution and more colors than the VGA and SVGA cards at the time. However, it was only available for IBM machines. Many of these features were later incorporated by other video card manufacturers.


Monitors - Review

1. Environmentally, which is the most difficult to dispose of?

hard drives
power supplies


2. What should you use to clean the plastic cover on your monitor or PC? Choose all that apply.

lint free cloth
mild soap solution


3. Your monitor has a cable or cord that connects the monitor to a/an _________ that is installed in an expansion slot on the computer's motherboard.

video adapter
VGA connector
RJ-45 connector


4. The CRT is the picture tube of your monitor. CRT is an acronym for ____________.

Cathode Ray Tube
Cathode Radio Transmitter
Video Picture Tube
Calcidium Ray Transceiver


5. The individual dots that make up the actual picture on your computer's monitor are known as picture elements or pixels.


6. The number of pixels across the top of your screen times the number of pixels down the side will give you the total number of pixels used to draw the image. This is known as the monitor's ___________.

dot pitch
refresh rate
7. The Graphical User Interface or GUI (gooey) is one of the least popular computer interfaces.



8. The closer pixels are to each other, the sharper the image will appear. The distance between pixels on a monitor is called it's __________ .

refresh rate
dot pitch
resolution factor

9. IBM developed the first analog display adapter called the _________.
XGA (Extended Graphics Array)
CGA (Color Graphics Array)
VGA (Video Graphics Array)
SVGA (Super - VGA)


10. If you have an older computer, and see a DB-9 female connector on the back, it's probably a/an _______________.

VGA video connector
EGA/CGA video connector
XGA video connector
SVGA video connector


11. The number of times in one second that the image on a monitor is redrawn is called its ____________, and is measured in Hertz (Hz).

dot pitch
refresh rate
interlace factor


12. What kind of monitor has the electron gun scan every second line in a single pass?

Interlaced monitor
Non-interlaced monitor
SVGA monitor
17" monitor

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