Measuring data center power efficiency is a critical aspect of understanding Green Computing and your ability to run a Green Data Center. There are three new tools for measuring the efficiency of how much power you use, and how much is actually being driven to the IT hardware, and not used for other tasks. Power Utilization Efficiency (PUE), Data Center Infrastructure Efficiency (DCiE), and SI-POM are the most common ways to ascertain the metrics concerning how much power used in the data center is being used to power IT hardware, and how much is used for other tasks. The highly efficient data center cannot be run without these kinds of metrics that show actual usage levels and changes in how power is used.