Data centers are collections of computers that make up the back end of a system. A data center isn't necessarily connected to the Internet -- it can be an internal system within an organization or company. But the Internet relies on massive data centers that contain hundreds of thousands of computers.
A data center could house database computers, Web servers and mainframes or some combination of all three. Several years ago, it was common for businesses to maintain their own data centers. Some were huge -- the size of a warehouse and filled with thousands of computers mounted in racks. Others were tiny and consisted of a single rack of machines.
Today, many businesses rely instead upon cloud services for their data center needs. This means they hire some other company to provide the physical devices upon which the business's data and services reside. Access to the business's information comes to us courtesy of the Internet. The cloud service data centers are truly massive with hundreds of thousands of machines stored in enormous buildings.
Cloud service companies will store a customer's data on multiple machines. This is for redundancy. If a computer fails for some reason, the customer's data remains intact because it exists on another machine. The downside of this arrangement is that each computer requires power to operate.
Computers also generate heat, which can be bad news. If electronic components get too hot, they can malfunction. To keep the machines operating at a safe temperature, data center owners must invest in cooling systems. The most common system is air conditioning. We should factor in the energy costs of air conditioning data centers in our final estimate since they are necessary to keep the Internet running.
Since 2008, the number of data centers in the United States has declined [source: IDC]. That's mostly due to companies shifting to the cloud-services model and offloading their data centers. But while there are fewer data centers, the ones that remain are growing larger. It's like trading a group of 50 hamsters for 10 elephants -- you have fewer animals in the end, but they take up a lot more room and use more energy.
Getting an exact count of data centers is impossible -- many companies keep information about their data centers private because it can be a competitive advantage. It's also impossible to say for certain how much power each data center requires without knowing all the details. That hasn't stopped people from trying. Next, we'll look at some of the methodologies people have used to estimate the Internet's power consumption.