One attraction of Power Usage Effectiveness (PUE) is the clear distinction it draws between productive power use (IT) versus non-productive overhead (e.g. non-IT) uses. We can extend the idea to other elements in the data center, like capital costs. While much of the capital cost of a data center is in the IT hardware, the infrastructure alone can cost from $10M to $20M per megawatt, depending on the design and construction of the data center. A significant part of that cost (10-20%) is the back-up generators, which are put in place as a last line of defense against power failure. It is capital that in the best case is never used!