Obviously it took them a while to get to warehouse scale, but I think they were thinking efficiently from the beginning, like using Legos and cheap racks to hold naked motherboards. http://infolab.stanford.edu/pub/voy/museum/pictures/display/... http://commons.wikimedia.org/wiki/File:Google%E2%80%99s_Firs...

Here's a photo set of the initial server rack, showing the use of 1/8'' cork sheets to separate circuit boards from contacting each other:

http://www.flickr.com/photos/nationalmuseumofamericanhistory...

In terms of the software, pretty much since the beginning. Even if Google only had 20 machines at first, the difference in mindset and software architecture is to treat each machine as expendable. The code has to be written very differently to account for that, and I think that was done starting fairly early.

In terms of the hardware, I guess it was a few years, whenever Google started building its own servers, building its own data centers, etc.

There are a lot of challenges as you scale, but it's safe to say that it wouldn't have made sense at any point to outsource/use AWS. New ground was being broken.