Microsoft has been building Mega Data centers at various cities in the World. To begin with Hotmail was already requiring such resources being the largest e-mail system in the world. As of this writing Windows Live-ID which is required for every hotmail account is the largest Identity provider (close to a billion Live-IDs have been created by end users) on the planet, far eclipsing any other identity system, irrespective of other fashionable fans.
You can read about the hotmail service at http://windowsteamblog.com/blogs/windowslive/archive/2009/12/22/a-peek-behind-the-scenes-at-hotmail.aspx
The size and scale of these Data Centers are just beyond our normal idea of what we call data centers. You can read more about these new Mega Data centers at the following links.
There is another huge data Center at San Antonio Texas and others to be added.
Now you might wonder why MS is on a path of rolling out these Mega Data Centers. Well the main reason is “Cloud Computing” as MS has made heavy investments in the Cloud computing viz the Windows Azure Services, as well as rolling out a host of hosted services where customers can host mission critical applications like their e-mail systems on MS Data centers. You might wonder if e-mail is indeed a mission critical app – yes it is. By an average most modern enterprises will shutdown if they cant have their e-mail systems 24X7.
In the cloud initiative, anyone can sign up for a Windows Azure account and develop applications and host it on Windows Azure which can be scaled up and down based on demand.