Yesterday Matt Davidson from JouleX, a data center energy management company, argued that power usage effectiveness (PUE) should be abandoned as a data center energy efficiency metric, a point of view I share. In its place Davidson suggests performance per watt (PPW). PPW is great in that it is straightforward and tells you how much actual compute a data center is doing for its energy use. No metric is perfect and one issue with PPW is that because there are so many different applications and server setups, it’s hard to establish baseline performance values against which to benchmark different data centers’ computing performance (to calculate PPW, you need standard measures of computing performance). That said, PPW at least allows us to shift the focus toward the ultimate outcome and purpose of a data center—the performance of the servers.