I think they use something called cloud computing, http://en.wikipedia.org/wiki/Cloud_computing , it's basicly millions of cheap computers all pooled collectively to deliver relivant info for searches(eg., http://www.nytimes.com/2007/10/08/technology/08cloud.html ).
Google must be extremely big... they even have a club of their own.. I believe there are more datacentres yet to be found
Looking at wikipedia we see that rapidshare is also big. Also wikipedia shows us how big the internet is.
the article details what computers they started on, it says IBM donated them they must be kicking themselves
And to think, once quantum computers are successfully created, one small laptop will be able to do the same work of those 500k+ servers.
Actually it's run on an Atari 800 with a million 5 1/4" floppy drives. Check it out, I snuck into the googleplex and got a picture of the floppy with their top secret algorithm on it... and to think, you wondered where all those old AOL floppies disappeared to
Imagine how much of these 450k servers contain spam and duplicated content (but rewritten in order to fool Google). I'm not wondering why Google penalizes and deindexes pages more and more often now, making it's webmaster guidelines more strict. They are constantly developing their algorythm.
I wonder how many of them are dedicated to indexing. And how many are just storage for site info that are already indexed, expecally their cache, tons of sites are stored on their servers.