There is a technical difference between shareware and demos. Up to the early 1990s, shareware could easily be upgraded to the full version by adding the "other episodes" or full portion of the game; this would leave the existing shareware files intact. Demos are different in that they are "self-contained" programs which are "not" upgradable to the full version. A good example is the Descent shareware versus the Descent II demo; players were able to retain their saved games on the former but not the latter.