What are data centers, and what do they do?

What is a data center?

The Congressional Research Service puts it simply: “In its simplest form, a data center is a physical facility that houses and runs large computer systems”[2]. Its fuller definition lists what fills that facility: computer servers, storage devices and networking gear, together providing the IT infrastructure to store, manage, process and transmit data at large scale[4].

In federal statistics, data centers fall within the data processing and hosting industry (NAICS 518), which the Bureau of Labor Statistics describes as establishments supplying the infrastructure for hosting and data processing services[7].

What does a data center do?

Three things, all day and all night: it stores data, processes it and moves it. The servers do the computing, the storage systems hold the data, and the network equipment carries it in and out of the building to the people and machines that asked for it[4]. When a company rents cloud computing, it is renting a slice of that capacity: CRS describes cloud data centers as interconnected facilities that let many users reach chips, software, storage and networks remotely[2].

The rest of the building exists to keep that work from stopping. Power comes in from the grid through a substation, the equipment that switches and regulates voltage[8]. Uninterruptible power supplies, essentially banks of batteries, protect the servers from outages[9], and on-site backup generators are designed to take over if the grid fails[4]. Because computers give off heat as a by-product of their work[10], cooling is the other big system: the Department of Energy says it can account for as much as 40% of a data center’s energy use[3].

That is why a data center’s size is often quoted in megawatts, the power it can draw, rather than in square feet. The International Energy Agency puts a conventional data center at around 10 to 25 megawatts[1]; a hyperscale, AI-focused one can be 100 megawatts or more[1].

The main types of data centers

The largest under construction as of 2025 will use 20 times as much electricity as a typical AI-focused data center, the IEA says[6]. What is an AI data center? covers the hardware, cooling and power in detail.

Why do we need data centers?

Because so much of what people do online runs on servers inside them. A 2023 Federal Reserve Bank of Richmond analysis tied the growth of data centers to demand for cloud computing that supports activities from online gaming to storing social media profiles[5]. Artificial intelligence has added a new, fast-growing source of demand: the IEA says AI models are trained and deployed in large, power-hungry data centers[6].

The scale of that reliance shows up in federal numbers. U.S. data centers used 176 terawatt-hours of electricity in 2023, 4.4% of the nation’s total, according to Lawrence Berkeley National Laboratory[11], and the number of people working in them grew from 306,000 in 2016 to 501,000 in 2023, per Bureau of Labor Statistics data reported by the Census Bureau[12].

That demand is also why data centers have become a local issue. They need a great deal of electricity, some need a lot of water, and where they are built matters to the towns around them. Why are data centers bad? sets out the criticisms and the evidence, and the rest of this site tracks the projects one by one.

What do data centers look like?

A typical data center is one large building. Virginia’s legislative auditors describe it as a 250,000-square-foot building[13], about the floor area of 4.3 football fields[14], and the state’s data centers together cover more than 63 million square feet on 7,200 acres of land[15]. Around the building sit the substation, cooling equipment and backup generators; local rules such as Fairfax County’s require that outdoor equipment be enclosed or screened by a wall, and that generators be kept 300 feet from residential lot lines unless the building shields them[16].

New campuses are far bigger than a single building. How big is a data center? compares real sites in acres and square feet.

What goes into choosing a location

Virginia's legislative audit agency, JLARC, attributes Northern Virginia's dominance to a strong fiber network, reliable and inexpensive energy, available land, proximity to major customers and a state tax incentive[13]. CRS adds that most developers prefer to buy power from the local utility and typically locate where existing utility supply is more readily available[4].

Where data centers came from

The idea is older than the internet. ENIAC, which Penn Engineering calls the first general-purpose electronic computer, was announced on February 14, 1946[17]; it filled a 30-by-50-foot room and had its own dedicated power lines[17]. When was the first data center built? traces the line from that room to today’s gigawatt campuses.

Common questions

What are data centers?

Buildings that house and run large computer systems: servers, data storage and network equipment used to store, process and move large amounts of data. They run cloud services, and they are where AI models are trained and deployed.

What does a data center do?

It stores, processes and moves data, and it supplies the power, backup power and cooling that keep its servers running without interruption. Cooling alone can take as much as 40% of a data center’s energy, according to the Department of Energy.

Why do we need data centers?

They run the cloud services behind everyday online activity, from gaming to social media, and they are where AI models are trained and deployed. U.S. data centers used 4.4% of the nation’s electricity in 2023.

What are data centers used for?

Companies use them to run their own computing, or rent space in colocation data centers; cloud providers use them to rent computing to many users at once; and AI developers use them to train and run models.

What is a hyperscale data center?

According to industry analysts cited by the Congressional Research Service, a hyperscale data center should contain at least 5,000 servers, occupy at least 10,000 square feet and have a power rating above 100 megawatts.

What do data centers look like?

A typical one is a single large building: Virginia’s legislative auditors describe it as 250,000 square feet, about 4.3 football fields, with a substation, cooling equipment and backup generators around it.

How big is an AI data center?

The IEA says a hyperscale, AI-focused data center can have a capacity of 100 megawatts or more, using as much electricity each year as 100,000 households. A conventional data center may be around 10 to 25 megawatts.

Sources

1. Understanding the energy-AI nexus – Energy and AI
   International Energy Agency · 2025-04-10
   2 source excerpts

   “A conventional data centre may be around 10-25 megawatts (MW) in size.”

   “A hyperscale, AI-focused data centre can have a capacity of 100 MW or more, consuming as much electricity annually as 100 000 households.”

2. Data Centers and Their Energy Consumption: Frequently Asked Questions (CRS R48646)
   Congressional Research Service (text via EveryCRSReport.com) · 2026-05-12
   6 source excerpts

   “To be considered a hyperscale data center, a facility should contain at least 5,000 computer servers and a large scale of network equipment and occupy at least 10,000 square feet of physical space, with an electric power rating, sometimes referred to as power draw, exceeding 100 megawatts (MW).”

   “In its simplest form, a data center is a physical facility that houses and runs large computer systems.”

   “Some online service providers operate geographically distributed and interconnected data centers and allow multiple users to remotely access computing resources such as data processing chips, software, data storage, networks, and applications hosted by these data centers, which are called "cloud data centers."”

   “For example, a large company may choose to build, own, and operate an on-premises data center (also known as an "enterprise data center") to house and manage its own IT infrastructure.”

   “Other organizations, especially those lacking the space, staff, or IT resources, often choose to rent a space, equipment, or services within a colocation data center (also known as a "managed data center") owned and operated by a third-party company.”

   “Cloud computing service providers may also operate and maintain smaller data centers physically located closer to end users (called "edge data centers") to reduce network latency and data communication delay, speed up content distribution, optimize real-time, data-intensive workloads, and improve application performance and user experience.”

3. DOE Announces $40 Million for More Efficient Cooling for Data Centers
   U.S. Department of Energy · 2023-05-09
   Source excerpt

   “data center cooling can account for up to 40% of data center energy usage overall”

4. Data Centers and the Electricity Grid: Frequently Asked Questions (CRS R49326)
   Congressional Research Service (text via EveryCRSReport.com) · 2026-09-01
   3 source excerpts

   “A data center is a physical facility housing computer servers, data storage devices, and network equipment that can provide information technology (IT) infrastructure services for storing, managing, processing, and transmitting large amounts of data.”

   “Data centers also typically have backup generators on-site designed to operate in case of a grid outage.”

   “Buying electricity from the local utility is the preferred option for most data center developers and is expected to remain so for the foreseeable future. Data center owners who prefer this option typically choose to locate their facilities in areas with more readily available existing utility electricity supply.”

5. Virginia's Data Centers and Economic Development (Econ Focus, Q2 2023)
   Federal Reserve Bank of Richmond · 2023-05-31
   Source excerpt

   “More recently, data center growth has been spurred by an explosion in the demand for cloud computing services to support activities ranging from online gaming to the storage of social media profiles.”

6. Energy and AI: Executive summary
   International Energy Agency · 2025-04-10
   2 source excerpts

   “Training and deploying AI models takes place in large and power-hungry data centres.”

   “A typical AI-focused data centre consumes as much electricity as 100 000 households, but the largest ones under construction today will consume 20 times as much.”

7. Data Processing, Hosting, and Related Services: NAICS 518 (Industries at a Glance)
   U.S. Bureau of Labor Statistics
   Source excerpt

   “Industries in the Data Processing, Hosting, and Related Services subsector group establishments that provide the infrastructure for hosting and/or data processing services.”

8. Glossary
   U.S. Energy Information Administration · 2026
   Source excerpt

   “Substation: Facility equipment that switches, changes, or regulates electric voltage.”

9. Uninterruptible Power Supplies
   ENERGY STAR (U.S. EPA) · 2026
   Source excerpt

   “An Uninterruptible Power Supply (aka a UPS Battery Backup) protects vital connected equipment -- computers, servers, and telecommunications equipment -- from power outages.”

10. High-Performance Computing Data Center Cooling System Energy Efficiency
    National Renewable Energy Laboratory (nrel.gov) · 2025-04-10
    Source excerpt

    “IT equipment, such as compute clusters and data storage systems, produces heat as a byproduct.”

11. 2024 United States Data Center Energy Usage Report
    Lawrence Berkeley National Laboratory · 2024-12-20
    Source excerpt

    “U.S. data center energy use has continued to grow at an increasing rate, reaching 176 TWh by 2023, representing 4.4% of total U.S. electricity consumption.”

12. Employment in Data Centers Increased by More Than 60% From 2016 to 2023 But Growth Was Uneven Across the United States
    U.S. Census Bureau · 2025-01-06
    Source excerpt

    “The number of people working in data centers grew from 306,000 to 501,000 between 2016 and 2023, according to the Bureau of Labor Statistics.”

13. Data Centers in Virginia (Report Summary)
    Joint Legislative Audit and Review Commission (JLARC), Virginia General Assembly · 2024-12-09
    2 source excerpts

    “Data center jobs tend to be high paying. Several data center representatives indicated that a typical 250,000-square-foot data center may have approximately 50 full-time workers, about half of which are contract workers.”

    “Multiple factors have contributed to Northern Virginia's market prominence, including a strong fiber network, supply of reliable cheap energy, available land, proximity to major national customers, and the creation of a state data center tax incentive.”

14. 2023 Official Playing Rules of the National Football League (Rule 1, Section 1)
    National Football League · 2023
    Source excerpt

    “The game shall be played upon a rectangular field, 360 feet in length and 160 feet in width.”

15. Data Centers in Virginia (Report 598)
    Joint Legislative Audit and Review Commission (JLARC), Virginia General Assembly · 2024-12
    Source excerpt

    “In total, Virginia has over 63 million square feet of data center space on 7,200 acres of land.”

16. Board of Supervisors Approves New Data Center Zoning Ordinance Amendment
    Fairfax County Government News Center · 2024-09-10
    2 source excerpts

    “In all districts where data centers are allowed, all equipment must be enclosed or screened by a wall or similar barrier to reduce visual and noise impacts.”

    “Equipment such as back-up generators must be 300 feet from the lot line of residential property or separated from the lot line of a residential district or residential property by the data center building.”

17. ENIAC
    Penn Engineering, University of Pennsylvania
    3 source excerpts

    “Originally announced on February 14, 1946, the Electronic Numerical Integrator and Computer (ENIAC), was the first general-purpose electronic computer.”

    “When fully operational, ENIAC occupied a room 30 by 50 feet in size and weighed 30 tons.”

    “ENIAC also had its own dedicated power lines and used 150 kilowatts of electricity.”

Each source was opened and checked against the excerpt shown. Company statements are identified as such. Figures are as published; where sources differ, each is shown.