They're not "allowed" to expire, they have an inherent time limit. Of course, smart patent holders make "improvements" and get new patents before that happens.

They're not "allowed" to expire, they have an inherent time limit. Of course, smart patent holders make "improvements" and get new patents before that happens. On the printer market: maybe you mean the laser printer? The 9700 came out in 1977, and the other laser printers a few years after. PARC was founded in 1970. There was also an antitrust settlement that Xerox made, which forced them to license the patents to competitors before they expired.