The basics
What is a data center, and what does it do?
A data center is a building full of computers that run around the clock. When you send an email, stream a show, pay a bill online, check a map or ask an AI chatbot a question, the work is usually done in a data center, not on your phone. This page explains what happens inside one and how it connects to the power grid and the Internet.
What a data center does
The U.S. Department of Energy’s Lawrence Berkeley National Laboratory defines a data center as “a facility used to house computer systems and associated components,” “primarily designed for data storage and processing.” They range “from small setups in closets to massive warehouses with thousands of servers.”
A server is a powerful computer without a screen or keyboard. Servers are stacked in tall metal cabinets called racks, and racks fill large rooms called data halls. Everything else in the building — power equipment, batteries, generators, cooling and fiber-optic cables — exists to keep those servers running without interruption.
Government LBNL, Data Center Energy Usage Report: 2025 Update, glossary · LBNL 2024 report, p. 36
Your request’s round trip
What happens when you open a weather app or ask a chatbot a question. The illustration is simplified; real networks have many more steps.
- Your deviceA phone or laptop sends a request.
- Wi-Fi or cell towerThe request travels by radio to your home router or the nearest tower.
- Your internet providerCarries it over cable or fiber toward the wider Internet.
- Fiber backbone and exchange pointsLong-distance fiber lines carry data as light. At internet exchange points, different companies’ networks hand traffic to each other.
- The data centerServers find your files or compute the answer, then send the result back the same way.
Government Terms as defined by the NTIA (U.S. Commerce Department), Introduction to Broadband, slides 14, 17, 27: an internet exchange point is “a physical location through which Internet infrastructure companies such as ISPs connect with each other”; the backbone is “interconnected networks that transmit data between and across countries and continents”; fiber “transmits data via light waves.”
Inside a data center: power and data in, heat out
Three things flow into the servers — electricity, data and cool air or liquid — and nearly all the electricity leaves the building as heat. The illustration is simplified.
Power
Data
Cooling
Where the electricity goes
Engineers track efficiency with Power Usage Effectiveness (PUE): total electricity for the whole facility divided by the electricity used by the computing equipment. A PUE of 1.0 would mean every watt goes to computing. The Department of Energy calls 1.6 average, 1.4 good and 1.1 better. Uptime Institute’s 2025 industry survey found a weighted average of 1.54 worldwide, little changed for six years; facilities of 20 MW and larger averaged 1.44.
Government LBNL 2025 Update (31%, 2024) · Government International Energy Agency, Energy and AI in East Asia, 2026, ch. 2 (servers, cooling) · Government DOE, Best Practices Guide for Energy-Efficient Data Center Design, 2024, p. 29 · Industry Uptime Institute Global Data Center Survey 2025, p. 7
Is it all about AI?
No — but it is the fastest-growing part. In 2023, most U.S. data center electricity still went to everyday computing: email, websites, streaming, online shopping, banking, business software and storage. AI runs on special chips (mostly graphics processors, or GPUs) that use much more electricity per server, so AI accounts for most of the growth that forecasters project.
Worldwide, the International Energy Agency reports that data center electricity use rose 17% in 2025, while AI-focused data centers grew about 50%.
Government LBNL 2024 report, pp. 7, 49–50 · LBNL 2025 Update · Government International Energy Agency, 2026
Does a data center store my personal data?
Often, yes. Cloud email, photo backups, online banking, medical portals and social media keep their information on servers in data centers — sometimes in another state or country. The companies say so in their own privacy policies:
- Google: “we operate data centers located around the world to help keep our products continuously available for users,” and “your information may be processed on servers located outside of the country where you live.” (Industry Google Privacy Policy)
- Microsoft: “Microsoft may store and process your personal data in your region, the United States, and any other jurisdiction” where it or its contractors operate. (Industry Microsoft Privacy Statement)
Many data centers hold no consumer data at all. A colocation building may house a bank’s or a hospital’s own servers; an AI campus may mostly train models. Who owns the building is often not who owns the data inside it.
Kinds and sizes of data centers
| Kind | What it is | Examples |
|---|---|---|
| Enterprise | Run by a company or government “internally, for their own use” | A bank’s or university’s own server rooms |
| Colocation | Rents space, power and cooling so other companies can “host their hardware offsite” | Equinix, Digital Realty |
| Hyperscale | “Built by companies that deploy internet services and platforms at massive scale” | Amazon, Google, Meta, Microsoft campuses |
| Edge | “Network closets, server rooms, and micro-data centers” close to users | Small sites near cell towers or in cities |
Government Definitions quoted from LBNL 2024 report, pp. 35–36. Company examples are ours.
How big is a megawatt?
Data centers are measured by how much power they can draw, in megawatts (MW). The International Energy Agency says “a conventional data centre may be around 10–25 megawatts,” while “a hyperscale, AI-focused data centre can have a capacity of 100 MW or more,” using about as much electricity in a year as 100,000 households.
For a U.S. comparison: the average U.S. home bought 10,791 kilowatt-hours of electricity in 2022 (EIA). One megawatt running all year is 8,760,000 kilowatt-hours — about what 810 average U.S. homes buy in a year (our calculation). Data centers rarely run at full capacity, so actual use is usually lower.
Government International Energy Agency, Energy and AI, 2025 · Government U.S. Energy Information Administration, household electricity FAQ
How many are there?
No government agency publishes an official count of U.S. data centers. Lawrence Berkeley National Laboratory’s 2024 study mapped “over 3,000 data centers,” and commercial databases list more. Our Tracker lists the ones found in public, openly licensed data.
Nationally, data centers used an estimated 192 terawatt-hours of electricity in 2024 — 4.7% of all U.S. electricity — according to the Berkeley Lab’s 2025 update. Its 2030 projections range from 9.5% to 15.3%.
Government LBNL 2024 report, sec. 4 · LBNL 2025 Update
How a data center connects to the power grid
Small data centers plug into the same local power lines as other businesses. Large ones need their own connection. Dominion Energy, which serves Northern Virginia, says loads of “more than 50 megawatts” typically require “the extension of transmission lines and the construction of a new substation,” that such projects take one to two years, and that service is often added in stages. Who pays for those lines — the data center or other customers — is one of the main disputes covered on our Facts and Legislation pages.
Inside the fence, the Department of Energy lists the chain as utility service, switchboard and switchgear, backup generators, uninterruptible power supplies (often battery banks) and power distribution units that step voltage down for the servers.
Industry Dominion Energy, Data Center Requests · Government DOE Best Practices Guide, 2024, sec. 6
How data centers connect to the Internet
Data centers sit on fiber-optic lines run by several network companies, so traffic can keep flowing if one line is cut. They cluster where many networks meet. Northern Virginia is the best-known example: according to Loudoun County, MAE-East, “the first commercial Internet Exchange Point,” opened in the region in 1992, and the county had about 233 data center buildings as of March 2026.
A claim you may have seen: that “70% of the world’s internet traffic” passes through Northern Virginia. We found no primary source for that number. Loudoun County’s own fact sheet says only that “much of the world’s internet traffic” passes through.
Government Loudoun County, Data Centers: The Loudoun Story · Loudoun County fact sheet, 2026