Many video adapters support several different modes of resolution. All such modes are divided into two general categories: character mode (also called text mode) and graphics mode. 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, with characters and other shapes formed by turning on combinations of pixels.
Of the two modes, character mode is much simpler. Programs that run in character mode generally run much faster than those that run in graphics mode, but they are limited in the variety of fonts and shapes they can display. Programs that run entirely in character mode are called character-based programs.