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Devices and hardware

Data center

Summary

A data center is a building designed to house servers, storage and network equipment with the power, cooling and connections to keep them running around the clock; the servers behind websites sit in them. The web's first server was a single NeXT computer at CERN in 1990. Colocation and hosting buildings spread in the late 1990s, and in 2006 Google opened its first data center of its own and Amazon launched its EC2 cloud service. The IEA estimates data centers used about 1.5% of the world's electricity in 2024.

Web Building Encyclopedia · Devices and hardware · Last reviewed October 22, 2026 · 10 min read

What a data center is

A data center is a building, or a dedicated part of one, built to keep computers running around the clock. The International Energy Agency (IEA) defines data centers as facilities that house servers, storage systems and networking equipment, installed in racks, together with the systems that power and cool them.1

Every website depends on one. A domain name points, through the Domain Name System, to an IP address, and that address belongs to a machine running web server software. When someone rents web hosting, they are renting all or part of such a machine, and the machine sits in a data center with power, cooling and fast links to the rest of the internet.

Data centers come in three broad kinds, defined by who owns the building and who owns the computers inside:

  • On-premise (enterprise). A company runs its own facility for its own systems.
  • Colocation. A company rents space, power and network connections in someone else’s building and installs its own equipment there. Equinix, one of the largest colocation firms, described its sites in 2003 as hubs where internet businesses place their equipment to connect with one another.2
  • Hyperscale. Very large sites run by the biggest cloud and internet companies for their own services and for cloud customers.

Synergy Research Group, which tracks the industry, estimated in April 2026 that hyperscale operators held 48% of the world’s data center capacity at the end of 2025, colocation firms 20% and on-premise sites 32%. It forecast that the hyperscale share would reach 67% by 2031.3

Inside a data center: power, cooling and network

A data center has three jobs beyond holding the computers: keep the power on, take the heat away and connect the machines to the outside world.

Power and the tier system

Servers cannot wait for the grid to come back after a blackout. Data centers bridge the gap with a UPS (uninterruptible power supply, banks of batteries or similar equipment that carry the load for the seconds or minutes until engine generators start) and with the generators themselves.4

The best-known way of rating this resilience is the Tier Classification System from the Uptime Institute, which created it more than 30 years ago. It has four levels:4

  • Tier I. Basic capacity: a UPS, a dedicated IT space, cooling and an engine generator. Maintenance needs a full shutdown.
  • Tier II. Adds redundant power and cooling components, so some parts can be taken out without stopping the site.
  • Tier III. Concurrently maintainable: redundant distribution paths mean any part can be shut down for maintenance without affecting the computers.
  • Tier IV. Fault tolerant: several independent, physically isolated systems, so a single equipment failure does not interrupt the computers.

Uptime says it has issued more than 4,300 Tier certifications in over 120 countries, and it stresses that a higher tier is not automatically better: each level suits different business needs.4

Cooling

The electricity that servers use ends up as heat, so cooling is a large part of a data center’s design. ASHRAE, the American engineering society for heating, refrigeration and air conditioning, publishes thermal guidelines for data processing environments. Its 2021 guidelines recommend an air temperature of 18 to 27 °C (64.4 to 80.6 °F) for its equipment classes A1 to A4.5

The amount of heat per rack is rising. In Uptime Institute’s 2026 global survey, the average of the most typical rack densities passed 11 kW (kilowatts, thousands of watts) for the first time, up from 9 kW in 2025, and 24% of respondents had racks drawing 30 kW or more, up from 19%.6

Network

The third job is connectivity. Large data centers bring in fiber from several network carriers, so that traffic can reach the internet by more than one route. Equinix’s 2003 annual report called its sites neutral because the company did not run a network of its own, and said it had relationships with the leading carriers.2 As of October 2026, Equinix lists 282 data centers on six continents and about 522,000 interconnections, direct cable links between customers.7

From one machine at CERN to internet data centers

The World Wide Web began on a single computer. By the end of 1990, Tim Berners-Lee had the first web server running at CERN, on a NeXT computer. A handwritten sign in red ink told staff that the machine was a server and must not be powered down.8 That machine, which hosted the first website, is still at CERN.9 The laboratory now runs its own data center, which its website describes as having 450,000 processor cores and 10,000 servers running 24 hours a day.10

As the web grew in the 1990s, companies began building facilities to hold other organizations’ internet equipment. Two companies founded in 1998 show the two directions this took:

  • Colocation. Equinix was incorporated in Delaware in June 1998 and built what it called Internet Business Exchange hubs, where networks and internet businesses could connect in one place.2
  • Content delivery. Akamai grew out of a challenge Tim Berners-Lee set his colleagues at MIT in early 1995: to find a new and better way to deliver internet content as the web became congested. Tom Leighton and Danny Lewin incorporated the company on August 20, 1998, and it launched commercial service in April 1999.11

The boom also produced hosting firms that built data centers for other companies’ websites. Exodus Communications offered managed hosting from what it called dozens of Internet Data Centers in North America, Europe and Asia Pacific.12 After the dot-com bubble burst, Exodus filed for Chapter 11 bankruptcy protection on September 26, 2001.12 Computerworld reported that GE Capital would provide up to $200 million in financing and that the company planned to keep serving customers without interruption.13

Cloud, hyperscale and the edge

Large internet companies also built their own. Google says it opened its first data center in The Dalles, Oregon, in 2006.14 The same year, on August 24, 2006, Amazon Web Services (AWS) launched EC2 in beta, a web service that “provides resizable compute capacity in the cloud,” so that customers could rent computing power in Amazon’s data centers instead of buying servers.15

On April 7, 2011, Facebook published the designs of its new data center in Prineville, Oregon, through what it called the Open Compute Project. It released specifications for servers, racks and battery cabinets, along with the building’s electrical and mechanical designs. Facebook said the site used 38% less energy for the same work as its older facilities and cost 24% less, and that one of its design choices was reusing hot air from the servers to heat offices in winter.16

Synergy Research Group counted 1,360 large data centers run by hyperscale companies at the end of 2025.3 A cloud provider groups its sites into regions. AWS describes an Availability Zone as one or more discrete data centers with separate and redundant power, networking and connectivity, placed up to about 60 miles (100 km) from the other zones in its region so that one disaster is unlikely to hit them all.17 As of October 2026, AWS lists 39 regions with 124 Availability Zones, with two more regions announced, in Saudi Arabia and Chile.18

Alongside these large sites are smaller edge locations, placed close to visitors. A content delivery network (CDN) keeps copies of pages, images and video in many of them. As of October 2026, AWS lists more than 750 points of presence for its CloudFront CDN.18 Cloudflare lists data centers in 348 cities and says 95% of the world’s internet-connected population is within 50 milliseconds of one of them.19

Distance matters because signals take time to travel. Google Cloud’s guidance for choosing a region estimates about 1 millisecond of round-trip delay for every 100 km, and notes that real network paths are often 1.5 to 2 times the distance on a map.20

Energy, efficiency and reporting rules

Power usage effectiveness

The standard measure of a data center’s efficiency is power usage effectiveness (PUE): the total energy the facility uses divided by the energy that reaches the computing equipment. A PUE close to 1.0 means nearly all the energy is used for computing, with little spent on cooling, lighting or power losses.2122

The industry group The Green Grid described PUE in early 2007, in its first white paper, on metrics for data center power efficiency.2324 The metric later became an international standard, ISO/IEC 30134-2, first published in April 2016.25 A second edition replaced it in January 2026.2225

Uptime Institute’s 2026 survey put the industry average PUE at 1.52. It said the figure dropped sharply between 2007 and 2014 and has improved only slowly since, in what it called a seven-year trend of relative stasis.6 Large operators report lower figures. Google says the fleet of data centers it runs had an average annual PUE of 1.09 in 2025, and lists the same 1.09 trailing twelve-month figure for the second quarter of 2026.21 Facebook reported an initial PUE of 1.07 for Prineville in 2011, against an average of 1.5 for its older facilities.16

How much electricity data centers use

In its Energy and AI report of April 10, 2025, the IEA estimated that data centers used about 415 terawatt hours (TWh) of electricity in 2024, about 1.5% of the world’s total. It projected that use would more than double to about 945 TWh by 2030, just under 3% of global demand, in its base case.126 The IEA said consumption had grown by 12% a year over the previous five years, and that in the United States, data centers are on course to account for almost half of the growth in electricity demand up to 2030.126

For the United States, a report by Lawrence Berkeley National Laboratory, dated December 19, 2024, estimated use over the decade.27 The U.S. Department of Energy announced it on December 20, 2024: data centers used 58 TWh in 2014 and 176 TWh in 2023, about 4.4% of all U.S. electricity, and could use 325 to 580 TWh by 2028, or about 6.7% to 12%.28

Reporting rules in the European Union

The European Union now requires larger data centers to report efficiency figures. Commission Delegated Regulation (EU) 2024/1364, adopted on March 14, 2024, applies to operators of data centers with an installed IT power demand of at least 500 kW. They had to send a first report by September 15, 2024, and must report by May 15 each year after that. The indicators include PUE, water usage effectiveness (WUE), an energy reuse factor and a renewable energy factor.29

When data centers fail

Uptime Institute’s 2026 survey found that 47% of operators had an impactful outage in the previous three years. Power was the main cause of the most damaging incident for 56% of them, and 19% of those reporting a significant, serious or severe outage put its cost at more than $1 million.6 Its outage analysis of May 13, 2026, said per-site outage rates had fallen for the fifth year in a row but more slowly, and that third-party operators such as cloud, telecom and colocation companies accounted for about two-thirds of publicly reported outages over nine years of tracking.30

The OVHcloud fire, 2021

Early on March 10, 2021, fire broke out at the Strasbourg site of OVHcloud, a large European host. OVHcloud gave the time as 00:47 and said its SBG2 building was destroyed, along with the 14,046 servers running in it, while some rooms of the neighboring SBG1 were also lost.31 The fire service report, as summarized by The Register, gives the time as 00:46 and traces the fire to electrical equipment on SBG2’s first floor; it also says the building had no automatic fire extinguishing system.32 The two sources differ by one minute.

The internet monitoring company Netcraft counted about 3.6 million websites, on 464,000 distinct domains, that were taken offline by the fire.33 On April 23, 2021, OVHcloud said all bare metal, VPS (virtual private server) and public cloud services in its two other Strasbourg buildings, SBG3 and SBG4, had been restored.31

The AWS outage in Northern Virginia, 2025

Failures do not have to be physical. From 11:48 PM Pacific time on October 19, 2025, to 2:20 PM on October 20, AWS services in its Northern Virginia (us-east-1) region were disrupted. AWS traced the cause to a “latent race condition” in the automated system that manages DNS records for its DynamoDB database service, which left the service’s regional address with an empty DNS record. The problem spread to other services, including new server launches, although servers already running stayed healthy.34

Timeline

  1. Uptime Institute's 2026 survey puts the industry average PUE at 1.526
  2. Synergy Research counts 1,360 hyperscale data centers at the end of 20253
  3. Second edition of the ISO/IEC 30134-2 PUE standard is published22
  4. A DNS fault disrupts AWS services in its Northern Virginia region34
  5. IEA estimates data centers used about 415 TWh of electricity in 20241
  6. U.S. Department of Energy reports data centers used 4.4% of U.S. electricity in 202328
  7. EU adopts Delegated Regulation 2024/1364 on data center reporting29
  8. Fire destroys OVHcloud's SBG2 data center in Strasbourg31
  9. ISO/IEC 30134-2 makes PUE an international standard25
  10. Facebook launches the Open Compute Project with its Prineville designs16
  11. Amazon Web Services launches EC2 in beta15
  12. Google opens its first data center, in The Dalles, Oregon14
  13. Hosting company Exodus Communications files for Chapter 1112
  14. Akamai is incorporated; commercial service follows in April 199911
  15. The first web server runs on a NeXT computer at CERN by the end of the year8

What it means for your website

Most small business sites never deal with a data center directly. Hosted builders such as Wix, Squarespace and Shopify choose the buildings for you. If you run self-hosted WordPress or rent a server, these questions are worth asking.

  • Where is the server? Ask your host which data center or region your site runs in, and pick one near most of your customers. Google Cloud’s rule of thumb is about 1 millisecond of round-trip delay per 100 km.20 Our guide to domains and hosting covers what else to ask before you buy web hosting.
  • Use a CDN for distant visitors. A CDN serves copies of your pages from edge locations close to each visitor, which shortens that distance.19
  • Keep backups somewhere else. When OVHcloud’s SBG2 building burned, 14,046 servers were destroyed with it.31 The WordPress handbook recommends at least three recent backups, stored in different places, for example one on the server, one in cloud storage and one on your own computer.35
  • Read the uptime promise. Tier ratings describe a building’s design, not a guarantee for your site, and Uptime Institute says a higher tier is not automatically better.4 Check the host’s uptime commitment and what it pays back if it misses.
  • Know where personal data goes. If you collect data from people in the European Economic Area, the EU’s data protection rules require safeguards when that data is transferred outside it.36 Our GDPR entry explains the basics; this is general information, not legal advice.

See also

References

  1. Energy demand from AI (Energy and AI report). International Energy Agency. 2025-04-10. accessed October 22, 2026.
  2. Equinix, Inc. Form 10-K for fiscal year 2002. Equinix, via U.S. Securities and Exchange Commission (EDGAR). 2003. accessed October 22, 2026.
  3. Hyperscale Operators to Account for 67% of all Data Center Capacity by 2031. Synergy Research Group. 2026-04-07. accessed October 22, 2026.
  4. Tier Classification System. Uptime Institute. accessed October 22, 2026.
  5. 2021 Equipment Thermal Guidelines for Data Processing Environments (reference card). ASHRAE Technical Committee 9.9. 2021. accessed October 22, 2026.
  6. Uptime Institute Global Data Center Survey 2026 (UII Keynote Report 209). Uptime Institute. 2026-07. accessed October 22, 2026.
  7. About Equinix. Equinix. accessed October 22, 2026.
  8. A short history of the Web. CERN. accessed October 22, 2026.
  9. NeXT server (Computer Centre visit point display). CERN IT Department. accessed October 22, 2026.
  10. The CERN Data Centre. CERN. accessed October 22, 2026.
  11. Company history. Akamai Technologies. accessed October 22, 2026.
  12. Exodus Communications, Inc. Form 8-K (Chapter 11 filing and press release). Exodus Communications, via U.S. Securities and Exchange Commission (EDGAR). 2001-09-27. accessed October 22, 2026.
  13. Exodus files for bankruptcy protection. Computerworld. 2001-09-27. accessed October 22, 2026.
  14. The Dalles, Oregon. Google Data Centers. accessed October 22, 2026.
  15. Announcing Amazon Elastic Compute Cloud (Amazon EC2), beta. Amazon Web Services. 2006-08-24. accessed October 22, 2026.
  16. Building Efficient Data Centers with the Open Compute Project (Jonathan Heiliger). Engineering at Meta (Facebook). 2011-04-07. accessed October 22, 2026.
  17. Availability Zones (AWS Fault Isolation Boundaries whitepaper). Amazon Web Services. accessed October 22, 2026.
  18. AWS Global Infrastructure. Amazon Web Services. accessed October 22, 2026.
  19. The Cloudflare global network. Cloudflare. accessed October 22, 2026.
  20. Best practices for Compute Engine regions selection. Google Cloud documentation. accessed October 22, 2026.
  21. Efficiency: power usage effectiveness. Google Data Centers. accessed October 22, 2026.
  22. ISO/IEC 30134-2:2026, Data centres key performance indicators, Part 2: Power usage effectiveness (PUE). International Organization for Standardization. 2026-01. accessed October 22, 2026.
  23. Green Grid releases datacenter efficiency white papers. insideHPC. 2007-02. accessed October 22, 2026.
  24. WP #1 Green Grid Metrics: Describing Data Center Power Efficiency. The Green Grid. 2007-01-27. accessed October 22, 2026.
  25. ISO/IEC 30134-2:2016, Data centres: key performance indicators, Part 2: Power usage effectiveness (PUE). International Organization for Standardization. 2016-04-19. accessed October 22, 2026.
  26. AI is set to drive surging electricity demand from data centres while offering the potential to transform how the energy sector works. International Energy Agency. 2025-04-10. accessed October 22, 2026.
  27. 2024 United States Data Center Energy Usage Report (Arman Shehabi and others). Lawrence Berkeley National Laboratory. 2024-12-19. accessed October 22, 2026.
  28. DOE Releases New Report Evaluating Increase in Electricity Demand from Data Centers. U.S. Department of Energy. 2024-12-20. accessed October 22, 2026.
  29. Commission Delegated Regulation (EU) 2024/1364 on the first phase of the establishment of a common Union rating scheme for data centres. Official Journal of the European Union, EUR-Lex. 2024-03-14. accessed October 22, 2026.
  30. Uptime Announces Annual Outage Analysis Report 2026 (Business Wire release). Uptime Institute, via ITWeb. 2026-05-13. accessed October 22, 2026.
  31. Updated information on the situation in Strasbourg (Spanish edition). OVHcloud. 2021-04-23. accessed October 22, 2026.
  32. OVHcloud datacenter 'lacked' automatic fire extinguishers, electrical cutoff (Thomas Claburn). The Register. 2022-03-22. accessed October 22, 2026.
  33. 3.6 million websites taken offline after fire at OVH datacenters (Paul Mutton). Netcraft. 2021-03. accessed October 22, 2026.
  34. Summary of the Amazon DynamoDB Service Disruption in the Northern Virginia (US-EAST-1) Region. Amazon Web Services. 2025-10. accessed October 22, 2026.
  35. WordPress Backups. Advanced Administration Handbook, WordPress.org. accessed October 22, 2026.
  36. Rules on international data transfers. European Commission. accessed October 22, 2026.

Web Building Encyclopedia. First published October 22, 2026. Last reviewed October 22, 2026. Every fact on this page is linked to a source we opened. Spotted an error? Write to [email protected].