A data center is a facility used for housing a large amount of electronic equipment, typically computers and other communications gear. Although they vary in size, a big tech company (a Microsoft, a Google) might have well over 100,000 computers in a single location. Obviously, with all those machines in one place, they use a lot of power. And as the demand for power increases, companies are now on a worldwide seek to find the cheapest, most sustainable supply of go-juice to run their operations.
Not surprisingly, there aren't a lot of places left in the world that have enough surplus energy to run an extra 100,000 computers. Iceland, with its massive amount of clean, geothermal power, has recently popped up as a potential candidate and both Cisco and Microsoft are investigating the possibility of establishing server farms in the Land of Fire and Ice. Otherwise, options are limited - forget about running a data center anywhere in the UK, energy is far too expensive there. And Manhattan is out, as there is literally no more room on the roofs for cooling. Sioux Falls, South Dakota might be an option, or maybe Winston-Salem, North Carolina - oops, Google already took that last one.