The Lunch Table: Are Apples Really More Energy Efficient Than Dells?

Occasionally, we will post informal commentaries based on the lunch-time conversations around our conference table. Some may wander into marketing, engineering, politics, or psychology, but they’ll always be focused on energy.


Here’s the true sign that you’re at an energy-geek conference: instead of the usual schwag like a logo sweatshirt or carry-on bag, the organizers hand out Kill-A-Watts. (A Kill-A-Watt, pictured below, is a small device that you can plug into a normal outlet to measure the electricity used by whatever you plug into the device.)  This is exactly what we did several years ago at our summer research workshop.


Our Kill-A-Watts helped settle a recent lunch-time bet. Severin had plugged his home computer, a Dell, into his Kill-A-Watt and checked it after he’d turned off the monitor and stopped using the computer: 50 Watts. My husband, who was convinced by our kids to buy an iMac several years ago, thought he had noticed a drop in our monthly electricity bills after we made the switch. (We leave our computer on all the time, a habit we adopted as PC users since it could take so long to reboot.) I wagered on my husband’s off-hand impression and bet Severin that our iMac used less power when not in use.

Well, it turns out that the iMac was far, far superior, in a way that even annoying Apple aficionados may not realize. Ten minutes after my son and I had stopped using the computer, it was drawing 1 Watt, one FIFTIETH the power of the Dell.


My son figured out that, compared to a PC, we were saving a dollar every three and a half days. Sure that’s less than his allowance, but real money nonetheless.


I asked several colleagues why this might be the case. Here’s the explanation that makes the most sense to me, courtesy of David Jacobowitz, who knows more than most about computer energy efficiency:

When a machine is “asleep” (technically, “suspended”) the processor is stopped and most peripherals are turned off. The hard drive is stopped. Only the memory is being refreshed to keep it from losing data. The result is that the machine should draw very near nothing. I have measured a lot of machines in sleep mode and not a single one was over 1.5 W, Apple or otherwise.On the other hand, Apple selects higher quality power supplies than most PC manufacturers and in general spends more time to make sure all the peripherals don’t interfere with sleep (a common problem — a peripheral or device driver forces the machine to remain awake).

So, it sounds like the iMac may be better at putting itself to sleep, while the Dell is more of an insomniac.


If you’re technically inclined, you can tell your computer when to go to sleep by adjusting the power management settings.


Is this another victory for Apples? How much does the manufacturer matter? It sounds like they matter a little, but they’re not the whole story. For one, manufacturers choose the default power management settings, which the vast majority of us never change. Also, the user interface may influence how many of us venture to change the power management settings, so the operating systems could make a difference. Finally, the speed with which the computer “wakes up” from sleep mode impacts how willing we are to put the computer to sleep in the first place.


Surprisingly, EnergyStar ratings, which are supposed to help consumers make decisions about the energy efficiency of their purchases, are just beginning to address sleep mode for computers. We can discuss the economics behind EnergyStar in another post, but this certainly seems like an area where information from the government could help consumers save energy and money.

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