Its not just computers,
its a phenomenon I call accelerated exponential evolution,
Things used to take 20 years or more between improvements/revolutions then as technology engineering and manufacturing progressed and understanding became more evenly spread,
progress itself became easier to accomplish so more people were progressing faster and sharing the knowledge which in turn made more of the species by proxy smarter
with more and more people working on projects, things got even faster and things took a little less time to be 'improved' upon, 15 years say,
then ten, then five and eventually we hit the limits of possibility with current materials/manufacturing, so we improve those to accomplish what we need them to or find/invent new materials that fit the bill,
I dont want to do anyones homework for them but your question cannot be answered in a simple statement so asking in these (or any other computer sites) forums wont get you the answers you want/need
you need to look into things in a bit of depth and discover what it was that made X or Y leap in development possible
Sorry, but nothing good comes easy man,
Moto