How Computer Monitors Work

by Jeff Tyson and Carmen Carmack
1. Introduction to How Computer Monitors Work

Because we use them daily, many of us have a lot of questions about our monitors and may not even realize it. What does "aspect ratio" mean? What is dot pitch? How much power does a display use? What is the difference between CRT and LCD? What does "refresh rate" mean?

2. Display Technology

Often referred to as a monitor when packaged in a separate case, the display is the most-used output device on a computer. The display provides instant feedback by showing you text and graphic images as you work or play.

Most desktop displays use liquid crystal display (LCD) or cathode ray tube (CRT) technology, while nearly all portable computing devices such as laptops incorporate LCD technology. Because of their slimmer design and lower energy consumption, monitors using LCD technology (also called flat panel or flat screen displays) are replacing the venerable CRT on most desktops.

Standards and Resolution

Resolution refers to the number of individual dots of color, known as pixels, contained on a display. Resolution is expressed by identifying the number of pixels on the horizontal axis (rows) and the number on the vertical axis (columns), such as 800x600. Resolution is affected by a number of factors, including the size of the screen.

As monitor sizes have increased over the years, display standards and resolutions have changed. In addition, some manufacturers offer widescreen displays designed for viewing DVD movies.

Common Display Standards and Resolutions

Standard	Resolution	Typical Use
XGA (Extended Graphics Array)	1024x768	15- and 17-inch CRT monitors 15-inch LCD monitors
SXGA (Super XGA)	1280x1024	15- and 17-inch CRT monitors 17-and 19-inch LCD monitors
UXGA (Ultra XGA)	1600x1200	19-, 20-, 21-inch CRT monitors 20-inch LCD monitors
QXGA (Quad XGA)	2048x1536	21-inch and larger CRT monitors
WXGA (Wide XGA)	1280x800	Wide aspect 15.4-inch laptops LCD displays
WSXGA+ (Wide SXGA plus)	1680x1050	Wide aspect 20-inch LCD monitors
WUXGA (Wide Ultra XGA)	1920x1200	Wide aspect 22-inch and larger LCD monitors

3. Aspect Ratio and Viewable Area

Two measures describe the size of your display: the aspect ratio and the screen size. Historically, computer displays, like most televisions, have had an aspect ratio of 4:3. This means that the ratio of the width of the display screen to the height is 4 to 3.
For widescreen LCD monitors, the aspect ratio is 16:9 (or sometimes 16:10 or 15:9). Widescreen LCD displays are useful for viewing DVD movies in widescreen format, playing games and displaying multiple windows side by side. High definition television (HDTV) also uses a widescreen aspect ratio.

All types of displays include a projection surface, commonly referred to as the screen. Screen sizes are normally measured in inches from one corner to the corner diagonally across from it. This diagonal measuring system actually came about because the early television manufacturers wanted to make the screen size of their TVs sound more impressive.

Interestingly, the way in which the screen size is measured for CRT and LCD monitors is different. For CRT monitors, screen size is measured diagonally from outside edges of the display casing. In other words, the exterior casing is included in the measurement as seen below.

CRT screen size

For LCD monitors, screen size is measured diagonally from the inside of the beveled edge. The measurement does not include the casing as indicated in the image below.

LCD screen size

Because of the differences in how CRT and LCD monitors are measured, a 17-inch LCD display is comparable to a 19-inch CRT display. For a more accurate representation of a CRT's size, find out its viewable screen size. This is the measurement of a CRT display without its outside casing.
Popular screen sizes are 15, 17, 19 and 21 inches. Notebook screen sizes are smaller, typically ranging from 12 to 17 inches. As technologies improve in both desktop and notebook displays, even larger screen sizes are becoming available. For professional applications, such as medical imaging or public information displays, some LCD monitors are 40 inches or larger!

Obviously, the size of the display directly affects resolution. The same pixel resolution is sharper on a smaller monitor and fuzzier on a larger monitor because the same number of pixels is spread out over a larger number of inches. An image on a 21-inch monitor with an 800x600 resolution will not appear nearly as sharp as it would on a 15-inch display at 800x600.