Talking to Cisco's Neil Walker about the relative efficiency (or inefficiency) of power-over-Ethernet versus individual mains adapters, I was reminded of a claim by eco-activists last year that only 5 percent of the power consumed by chargers actually goes into charging a mobile phone or MP3 player. The rest is wasted as heat, generated while the charger is plugged in but the device isn't.

And it's not just phone chargers - have a look around your desk and count the number of mains adapters generating heat. Within a few feet of my own, I can count at least six - the deskphone, mobile phone, PC speakers, powered USB hub, network print server and Ethernet switch all have their individual "power bricks".

Politicians, keen to buff up their green credentials, are already starting to notice. The US Environmental Protection Agency and the California Energy Commission have issued new rules on external power supplies, effectively banning simple transformer-type linear chargers in favour of smarter and more efficient switch-mode chargers. How long will it be before the legislators turn their attention to the huge amount of power wasted by IT?

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