"DOS"es are usually text-based and without graphics to save space on a floppy disk. Although DOSes have mostly been replaced by Windows, Macintosh, and Linux systems, among others (sporting a GUI, or Graphical User Interface), they are still in use in some places, mostly on older computers. This may be because of a lack of money, the need to use software which still runs on a DOS system, nostalgia for an older operating system, or the belief that text-based systems are more efficient.