Periodically Google sends out robots to crawls the web. It archives the web which it finds. These archived websites are presented in next update. The update is followed by the database or index which has been stored by Google. This process is initiated at every 30 days or more to update. The Google get its results from more than 10000 servers which are Linux PCs. The reason out that all the index cannot be updated at the same time. One after the other is updated with the new index.

It is supposed that Google has two test domains.

1. www2.google.com
2. www3.googl.com

These test domains have a stable DNS record which resolves only one IP address. Before the index update or Google Dance begins any one or at least one of the test domains is assigned the IP address of the center that receives the new index first.

So, the search results which are to be seen on www2.google.com and www3.google.com will always appear on www.google.com later on, as long as there is a regular index update. However, there may be minor fluctuations. On the one hand, the index at one data center never absolutely equals the index at another data center. We can easily check this by watching the number of results for the same query at the data center domains listed above, which often differ from each other. On the other hand, it is often assumed that the iterative Page Rank calculation is not finished yet, when the Google Dance begins so that preliminary values exert influence on rankings at that point in time.