Many video adapters support several different modes of resolution, all of which are divided into two general categories: character mode and graphics mode.
Of the two modes, graphics mode is the more sophisticated. Programs that run in graphics mode can display an unlimited variety of shapes and fonts, whereas programs running in character mode are severely limited. Programs that run entirely in graphics mode are called graphics-based programs.
In character mode, the display screen is treated as an array of blocks, each of which can hold one ASCII character. In graphics mode, the display screen is treated as an array of pixels. Characters and other shapes are formed by turning on combinations of pixels.