Data centers, like most of our economy, are going through a period of change and re-branding. 

In the stone age of data centers (circa 2005) we were able to put data centers on the street supporting somewhere around 100 watts per square foot.  This was considered really high density, supporting a vision for the next 10 years server farms and high capacity switching.

Of course that lasted all of about a year, and data center operators once again found themselves scrambling to figure out how to bring more power into the data center, and even more importantly how to bring enough cooling capacity into the data center to prevent servers and switches from burning up.