In September 1997, Computer published a special issue on billion-transistor microprocessor architectures. Comparing that issue's predictions about the trends that would drive architectural development with the factors that subsequently emerged shows a greater-than predicted emphasis on clock speed and an unforeseen importance of power constraints. From seven architectural visions proposed in 1997, none has yet emerged as dominant. However, as we approach a microrarchitectural bound on clock speed, the primary source of improved performance must come from increased concurrency. Future billion-transistor architectures will be judged by how efficiently they support distributed hardware without placing intractable demands on programmers.