Bit-mapped display

Bit-mapped displays are the current standard for output in user interfaces to computers. They provide a screen which has a array of pixels, each one of which can be independently set - in most contemporary units, to a color value set by three 8-bit values, one for each primary colour (red, green and blue).

Originally, before semiconductor RAM prices fell, bit-mapped dislays provided fewer bits per pixel; originally only one bit per pixel. (Some low-end or low-power displays still provide only this.) At an intermediate stage, an 8-bit value for each pixel was used: either for a grey-scale; or mapped into three 8-bit values per colour (i.e. only 256 distinct colours in use at any time, although each colour could be selected arbitrarily).

The resolution depends in part on the physical size of the screen; and in the early stages, on RAM cost. Some early displays were as little as 320×200; later on, 1024x768 pixels was widespread, and then 1280x1024. As the aspect ratio of high-definition television has become common, resolutions such as 1280×720 and 1920×1080 have become more common.

The original bit-mapped displays were an evolution of video terminals; once RAM prices fell low enough, the ability to display graphics, etc, instead of just characters, made the step forward inevitable.