For a brief account of the evolution of PDAs, see Anita M. McGahan, Leslie L. Vadasz, and David B. Yoffie, "Creating Value and Setting Standards: The Lessons of Consumer Electronics for Personal Digital Assistants," in David B. Yoffie (ed.), Competing in the Age of Digital Convergence (Boston: Harvard Business School Press, 1997): 227–264, especially pp. 230–240.