• Pixels are picture elements. The screen image is made of pixels (tiny dots), which are arranged in rows across the screen. Each pixel consists of three colors: red, green, and blue (RGB). Examine the screen closely to see them.
• Dot pitch is a measurement of how close together the phosphor dots are on the screen. The finer the dot pitch, the better image quality you will have. Look for the smaller number. Most monitors today have a 0.25mm dot pitch. Some have a 0.22mm dot pitch, which gives a very fine resolution.
• The refresh rate is the rate per seconds that the screen image is refreshed. Refresh rates are measured in Hertz (HZ), which means times per second. The higher the refresh rate, the more steady the screen image will be. It may look like a steady picture, but actually it flickers every time the electron beam hits the phosphor-coated dots. Refresh rate is also called vertical frequency or vertical refresh rate.
• Color Depth refers to the number of different colors each pixel can display. This number is measured in bits. The higher the depth, the more colors that can be produced.
• Video RAM (VRAM) is the memory used by a video card. How much they have determines the color depth setting available to the monitor. The more VRAM your video card has, the more colors that can be displayed. The video card also sends out the refresh signal, thus controlling the refresh rate.
• Resolution varies based on the number of pixels. The more pixels in the screen, the better the resolution. Better resolution means a sharper image. The lowest screen resolution on modern PCs is 640 x 480 pixels, which is called VGA (Video Graphics Array). There are now SVGA (Super Video Graphics Array) and XGA (Extended Graphics Array) with resolutions all the way up to 1600 x 1200.
• Monitor screen sizes are measured in inches, just like televisions. The most common sizes are 14," 15," 17," 19," and 21" screens, measured diagonally. Note that the visible size is actually smaller than the measurement size. Have this in mind when shopping for a monitor for the computer.
• Most PCs display many colors on the screen. The colors are created by varying the light intensity of the three basic colors (red, green, and blue). 24- and 32- bit colors are the usual choice for graphic artists and professional photographers. For most other applications, a 16-bit color will be sufficient. Figure gives a summary of the most commonly used color depths.

A high quality monitor and a high quality video card are required for both a high resolution and a high refresh rate.

Video Cards
The video card or video adapter is the interface between the computer and monitor. The video card tells the monitor which pixels to light up, what color the pixels should be and the intensity of the color. The video card is either an expansion card (installed into one of the motherboard expansion slots) or it can be built into the motherboard. The display capabilities of a computer depend on both the video adapter and the monitor. A monochrome monitor (black and white), for example, cannot display colors no matter how powerful the video adapter.

Following are some key terms related to video cards:

• It is important not to confuse the terms video memory and video RAM (VRAM). Video memory is a generic term used to refer to memory in the computer video system, while VRAM is a special type of memory used on video cards. Most modern video cards contain video RAM, which is a special form of DRAM that has two separate data ports. One port is dedicated to updating the image that is viewed on the computer screen, while the other port is used for changing the image data stored on the video card. Thanks to VRAM, the computer RAM is not being used for storing displays. A 64-bit AGP video card with 4 MB of RAM should be enough, but more graphic intensive games may perform better with a video card having 32 MB or more video RAM. Some video cards even include a graphics coprocessor for performing graphics calculations. These adapters are referred to as graphics accelerators. A newer form of VRAM is WRAM (Windows RAM). 
• The Pentium II has an Accelerated Graphics Port (AGP) expansion slot for installing a video card. AGP is designed exclusively for video cards. An AGP card allows game and 3D applications to store and retrieve finer, more realistic textures in system memory rather than video memory, without incurring any performance problems. A significant advantage of the AGP is that the PCI bus is relieved of handling graphics data, so that the PCI slot can concentrate on other demanding duties. AGP also doubles the PCI transfer speed.

Video adapters are also known as video cards, video boards, and video display boards. At a minimum, a video card should be a PCI adapter with at least 4 MB of RAM or more, depending on the type of graphics to be run.

Lab Activity  (PDF, 11 KB)   In this lab, students will be able to identify the video card by any markings on the card.