Set-top boxes supplied by cable companies are likely using more power than desktop and laptop computers, and about 25 per cent of the power used by a two-socket server.
More than 160 million set-boxes are in use in the U.S. A typical system with HD-DVR uses 446 kWh annually, according to a recent report by the National Resources Defense Council.
"These things [set-top boxes] never power down, so it's actually not surprising," said Mark Davidson, sustainability officer at JouleX, maker of energy management systems for data centers.
The set-top box industry is currently building devices with energy management improvements, and the council's report says that more recent models of set-top boxes with HD-DVR use about 275 kWh annually.
But in the aggregate, set-up boxes used 27 billion kWh of electricity in the U.S last year, the council said.
The last time aggregate power usage of all servers in the U.S. was studied was five years ago, so it's difficult to benchmark the overall power usage of set-top boxes. But in 2006, a government study put total power usage of all servers in the U.S. at about 24 billion kWh.
Davidson supplied some estimates on power usage for servers, desktops and laptops to make a comparison.
Newer, two-socket x86 servers with up to eight core chips will run at rest somewhere between 150 to 200 watts. At full utilization, this energy usage can double to as much as 400 watts.
In terms of annual energy usage , a two-socket server may use approximately 1,314 kWh a year (which is simply just powering it on) to about 2,600 kWh per year.
Allowing for variations in workload demand, the average annual power use for a two-socket server is around 1,800 to 1,900 kWh annually.
Servers are expected to run 24x7, which isn't necessarily true for most desktops and laptops. But if these systems did run continuously, here's how much power they will take up.
Desktops use between 45 watts and 90 watts, so if they ran 24x7 they would use between 394 kWh annually and 788 kWh annually.
A laptop running between 30 watts and 75 watts will use between 262 kWh annually and 657 kWh annually.
Davidson said power utilization continues to improve with new generations of semiconductors, which deploy technologies such as speed step to change the chip's clock rate dynamically to reduce power usage.
Energy consumption is estimated by using wattage x hours used per day / 1000 = daily kilowatt-hour (kWh) consumption.
Utility bills are calculated by number of kWh used by the cost. For instance, a system that uses 394 kWh x 8.5 cents/kWh, is costing $33.51 a year, according to the U.S. Environmental Protection Agency, which has a number of examples on its site.
Patrick Thibodeau covers SaaS and enterprise applications, outsourcing, government IT policies, data centers and IT workforce issues for Computerworld. Follow Patrick on Twitter at @DCgov , or subscribe to Patrick's RSS feed . His e-mail address is email@example.com .
Read more about data center in Computerworld's Data Center Topic Center.