What is a CRT Monitor?

CRT stands for cathode ray tube, describing the technology inside an analog computer monitor or television set. A CRT monitor or TV is readily recognizable by its bulky form. LCD monitors and plasma television sets, or flat panel displays, use newer digital technologies.

The CRT monitor creates a picture out of many rows or lines of tiny colored dots. These are technically not the same thing as pixels, but the terms are often used interchangeably. The more lines of dots per inch, the higher and clearer the resolution. Therefore 1024 x 768 resolution will be sharper than 800 x 600 resolution because the former uses more lines creating a denser, more detailed picture. Higher resolutions are important for displaying the subtle detail of graphics. For text, resolution isn't as critical.

But how do those colored dots appear on the screen?

Inside a CRT monitor is a picture tube that narrows at the rear into a bottleneck. In the bottleneck is a negative charged filament or cathode enclosed in a vacuum. When electricity is supplied, the filament heats up and a stream or "ray" of electrons pour off the element into the vacuum. The negatively charged electrons are attracted to positively charged anodes which focus the particles into three narrow beams, accelerating them to strike the phosphor-coated screen. Phosphor will glow when exposed to any kind of radiation, absorbing ultraviolet light and emitting visible light of fluorescent color. Phosphors that emit red, green and blue light are used in a color monitor, arranged as "stripes" made up of dots of color. The three beams are used to excite the three colors in combinations needed to create the various hues that form the picture.

To precisely direct the beams, copper steering coils are used to create magnetic fields inside the tube. The fields move the electron beams vertically or horizontally. By applying varying voltages to the steering coils, a beam can be positioned at any point on the screen. Each image is painted on the screen -— and repainted -- several times each second by scanning the electron beams across the screen at incredible rates. This must be done even when the picture being displayed is unchanging, because the phosphor only glows for a very short time.

The refresh rate indicates how many times per second the screen is repainted. Though monitors differ in their capabilities, lower resolutions normally have higher refresh rates because it takes less time to paint a lower resolution. Therefore a setting of 800 x 600 might have a refresh rate of 85Hz, (the screen will be repainted or refresh 85 times per second), while a resolution setting of 1024 x 768 may have a refresh rate of 72Hz. Still higher resolutions usually have refresh rates closer to 60Hz. Anything less than 60Hz is generally considered inadequate, and some people will detect "flicker" even with acceptable refresh rates. Generally speaking, high-end monitors have higher refresh rates overall than lower-end models.

Another specification regarding CRT monitors is "dot pitch" which relates to the tightness or sharpness of the picture. A lower dot pitch such as .25 is preferable over a higher dot pitch. In the heydey of the CRT monitor this was an issue because some models were sold with .32 dot pitch, resulting in "fuzzy" text. By the end of the CRT era, virtually all displays had .28 or better and today's CRT monitors can have dot pitches as low as .21.

The CRT monitor comes in 15-inch to 21-inch sizes (38 — 53 cm) and larger, though the actual viewing screen is about 1 inch (2.5 cm) smaller than the rated size. Screens are measured diagonally from corner to corner, including the case.

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