|Maintains an index or table of contents of information that can be found across a large distributed network, such as computers, users, files shared on file servers, and web apps. [[Directory server]]s and [[name server]]s are examples of catalog servers.
|Any computer program that needs to find something on the network, such as a [[Windows ___domain|Domain member]] attempting to log in, an [[email client]] looking for an email address, or a user looking for a file
|-
|[[Communications server]]
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== Energy consumption ==
In 20102024, data centers (servers, cooling, and other electrical infrastructure) consumed 415 [[Kilowatt-hour|terawatt-hours]] of electrical energy, and were responsible for roughly 1.1–1.5% of electrical energy consumption worldwide,<ref>{{Cite andweb 1.7–2.2%|last=magazine in|first=Sophia theChen, UnitedNature States.<ref>{{cite|title=Data Centers Will Use Twice as Much Energy by 2030—Driven by newsAI |url=https://www.nytimesscientificamerican.com/2011/08/01/technologyarticle/ai-will-drive-doubling-of-data-centerscenter-usingenergy-lessdemand-powerby-than2030/ |access-forecastdate=2025-report06-says.html?_r17 |website=0Scientific American |titlelanguage=Dataen}}</ref> Centersand Usingfor Less4.4% Powerin Thanthe Forecast,United ReportStates.<ref>{{Cite Saysreport |dateurl=31https://escholarship.org/uc/item/32d6m0d1 Jul|title=2024 2011United States Data Center Energy Usage Report |newspaperlast=[[NYHamm Times]]|first=Geoff |access-date=18 Jan 20132025 |firstpublisher=JohnLawrence Berkely National Laboratory |lastdoi=Markoff10.71468/p1wc7q}}</ref>{{Update inline|date=November 2023}} One estimate is that total energy consumption for information and communications technology saves more than 5 times its [[carbon footprint]]<ref>{{cite web |url=http://www.smart2020.org/_assets/files/02_Smart2020Report.pdf |archive-url=https://web.archive.org/web/20101122051650/http://www.smart2020.org/_assets/files/02_Smart2020Report.pdf |archive-date=22 November 2010 |title=SMART 2020: Enabling the low carbon economy in the information age |date=6 Oct 2008 |publisher=[[The Climate Group]] |access-date=18 Jan 2013 }}</ref> in the rest of the economy by increasing efficiency.
Global energy consumption is increasing due to the increasing demand of data and bandwidth.
Global energy consumption is increasing due to the increasing demand of data and bandwidth. [[Natural Resources Defense Council]] (NRDC) states that data centers used 91 billion kilowatt hours (kWh) electrical energy in 2013 which accounts to 3% of global electricity usage.<ref>{{cite web | url=https://lifelinedatacenters.com/data-center/reduce-data-center-carbon-footprints/ | title=How to Reduce Data Center Carbon Footprints | Lifeline Data Centers | date=12 February 2015 }}</ref>{{Update inline|date=November 2023}}
[[Environmental groups]] have placed focus on the carbon emissions of data centers as it accounts to 200 million metric tons of [[carbon dioxide]] in a year.
