Data centers use large amounts of power, and if they’re not operating efficiently, a lot of that energy is wasted. Like the mindless, shambling creatures from “The Walking Dead,” zombie servers use energy without actually doing anything. A June 2015 study from Jonathan Koomey of Stanford University and Jon Taylor of Antithesis Group estimated that one out of every three data centers is a zombie, also known as a “comatose server.” With data from TSO Logic, Koomey and Taylor identified the threats that these servers pose to enterprises.