Though small on-premise data centers house the majority of servers, the general trend is toward consolidation into increasingly larger facilities. The modern data center is a highly optimized computing machine compared with early-era server rooms, and yet considerable efficiency and conservation opportunities still exist in most facilities. Gains in energy-use optimization have largely resulted from efforts to reduce operating costs and maintain a competitive advantage in this rapidly evolving sector. Only within the past few years have energy efficiency and conservation become popular metrics by which data center operators are gauging their facility’s performance.