What's the Resolution?

Now that notebooks like the ThinkPad 760CD support resolutions higher than standard VGA (640 by 480 pixels), there's a complication with DOS applications that still display at 640 by 480 on an LCD screen. On a desktop CRT display, there's no problem because there's no hard-and-fast connection between logical resolution and the red, green, and blue phosphor triads that make up the image. The spacing of pixels is determined by modulation of the electron beam that writes the image on the inside surface of the screen ( see the figure ). It's an analog system.

But LCD displays are digital. Each pixel is a physical element: a transistor-controlled set of t hree LCD cells, each with its own color filter (again, red, green, and blue). To get 640 by 480 resolution on an 800 by 600 screen, either you wind up with a smaller image that occupies only the center part of the display or the graphics processor tries to scale the image up to fit the screen. This process works adequately for video images, but it makes text look funny because the scaling can't be smooth. Some lines are doubled, but some aren't.

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Pixels and Phosphor Dots

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With a CRT display, the size and placement of pixels are not related to the array of colored phosphor dots that produce the image. With an LCD, each pixel is a physical structure.