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As video displays have evolved from monochrome to CGA, EGA, VGA and SuperVGA, the amount of RAM needed on video cards has increased. This is because the main purpose of video RAM is to serve as a temporary storage place (frame buffer) for video data before it is sent to the display, and the amount of data to be stored has increased as the resolution and color depth of displays has increased. Resolution determines the number of picture elements (pixels) in the image and color depth determines the number of bytes of information (and thus the number of colors available) per pixel. Multiply these two together and you have a good estimate of the amount of video RAM needed for to generate a screen image in any particular video mode. The table below shows the RAM requirements for a variety of resolutions at both High Color (65,326 possible colors per pixel) and True Color (over 16 million possible colors per pixel). See the addendum below if you want to understand how these numbers were determined. Even though True Color provides an enormous amount of color possibilities, it does not require that much more RAM than High Color. Note that some video cards will not run True Color at 24 Bits but require 32 Bits, making their RAM requirements in True Color mode twice as high as High Color.
Except for some very uncommon RAM types, modern video cards come in configurations of 1MB, 2MB, 4MB or 8MB of video RAM. The color coding above shows the RAM needed (gray=1MB, yellow=2MB, turquoise=4MB, blue=8MB). Newer cards have 16 or even 32MB of video RAM. Note that the extra RAM above 8MB is not used for 2D displays but is used for texture storage, a z-buffer space in 3D modes. So, what do YOU need? First, determine the resolution at which you will run your monitor. There is some personal preference operating here - some people will think things look too small on the screen at higher resolutions, although in Win95/98 virtually everything on the desktop can be adjusted. As a general rule the most comfortable resolution at each nominal monitor size:
What about color depth? Unless you are doing photo-editing or graphics work as a professional, you will find that High Color provides excellent image quality. So, looking at the tables above you will see that for a 17" monitor you should get a minimum of 2MB video RAM, while a 19" should be supplied with 4MB of video RAM. Video RAM prices have fallen so rapidly over the past few years that 4MB RAM configurations are becoming the norm and very good video cards with 8MB RAM can be purchased for less than $100 to $150. Also, if the card you are considering combines 3D display functions, used primarily in video games, the video RAM needs will be higher in order to handle these functions. So, use these tables as a minimum guideline if you are on a tight budget and want to make sure you get at least what you need. ---------------------- Addendum: To calculate the RAM requirements you multiply the number of total number of pixel at the particular resolution times the number of bits of information per pixel. For instance, the most common video mode run now is 640x480 pixels or 307,200 total pixels for the screen, as shown in the table. Most people now at a color depth of 16-bits per pixel. 16-bits per pixel provides 65,536 colors possible colors per pixel and is known as High Color. Now, since 1 Byte is 8 bits, 16-bits is 2 Bytes. So, the amount of RAM required to store a 640x480,16-bit image would be 307,200 pixels times 2 Bytes per pixel, which equals 614,200 Bytes. To converts Bytes to MegaBytes (MB) requires one more technicality. Because of the binary basis of computers, one KiloByte (KB) actually equals 1,024 Bytes and one MB equals 1,024KB, so 600KB is 0.59 MB. Sorry about this math, but you can see that to display High Color mode at 640x480 requires just over one-half MB.
This page is last updated Saturday, January 08, 2000 |
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