How does Google work?

Google does not consist of one large database, producing consistent search engine rankings for all places at any one time. Google uses many different data centers, each one comprised of many thousands of servers, to store its search engine ranking data. Different data centers are used partly to cope with the volume of requests, but also possibly to enable modifications to algorithms to be checked on one data center without affecting the SERPS viewed by everyone.

Most of the time these data centers give similar search engine ranking positions (SERPS) but at times they produce very different search engine ranking positions. It has been observed that larger variations in SERPS between data centers often occur before a notable change to the Google ranking algorithm.