I measured electricity usage of our
home computers using a cheap clamp-on ammeter from Radio Shack. I
concluded that you need to make your own measurements because many of
my preconceptions did not hold up to actual measurement. Since then
I bought a more accurate and convenient Watts
Up meter for $21 from amazon.com, and re-measured everything.
colleagues at HP: I apologize for saying your PC used 300 watts.
100 watts is more like it. I likewise
overstated the power usage of other PC’s. I correct the measurements
here, along with some discoveries about Windows and Ubuntu power
management. You may be asking, why should I believe you now? Good
question. You should not believe some random person you find on the
net. You should get your own meter and measure your own equipment.
Why might you halfway believe me,
enough to read a bit more? Well, Watts Up does seem to be a more
reliable instrument, and unlike my earlier measurements it corrects
for the power factor. It displays the power factor, which can vary
greatly from one device to another. As a check on the new meter I
measured a 3-way light bulb: the 60w setting measured 44w, the 100w
setting measured 89w, and the 150w setting measured 135w. At least
I’m assured it’s not measuring high.
A colleague in the SPEC power committee
laughed at my new meter, “You mean you trust a Watts Up meter?”
For the upcoming SPEC power
benchmarks that team of engineers from many companies, universities,
and agencies has written elaborate requirements for the power meter
and measurement protocol to be sure that results tested by one lab
will be comparable to results tested by another lab. But for home, if you can get any information at all about the power your electronic gear uses, that’s good.
First I looked at how many watts they
used in normal home, light load operation. I switched the Linux
distro on PC2002 to Ubuntu 7.04 Feisty Fawn, and its power management
software seems to be the equal of Windows.
Next I looked at how many watts they
used under a heavy load. These weren’t identical controlled loads,
and workload really matters to how much power is used.
How much of difference does workload
make? Here is the power consumption of PC2002 running Ubuntu:
Watts (PC only)
download OS updates
100-Base-T file copies
80 – 100
Play Supertux arcade game
Scanning document with USB scanner and xsane
Afterwards [Note 1]
[Note 1] I don’t know what set off the
MySQL daemon, whether it was doing useful work, or had just run wild.
But without the power meter, had I noticed anything amiss at all, I
would have just been puzzled that the fan was running. When I stopped
the daemon, power usage fell back down to normal levels.
Next I suspended each PC by pressing
the sleep button as the system is configured out of the box.
But wait, what’s going on with that new
HP PC taking so much more power suspended than the old HP PC? I
looked at the Windows power management control panel and started
reading the documentation. It turns out that the old PC was set by
default for the sleep button to put it into what Windows calls
“standby” state, while the new PC was set by default for
the sleep button to put it into “away” mode. Away mode
doesn’t do much, and is intended for systems that might still be
doing some processing without a person sitting there. So it’s kind of
like forcing it immediately into the quiescent state it would
eventually go into if you just left it alone, and the monitor blanks.
I changed it to go into suspend state, and then it used just 6 watts.
Hibernate state used 4 watts. Michael Chu wrote a great
description of how Windows XP power management works.
Here are some details of my
|PC1999||Primary: Sun JDS3 Linux; Secondary Windows 98SE||PC, Sony Vaio, Pentium III, 500MHz||NEC, 14” LCD, 1024×768||Sony|
|M2000||Primary: Linspire Linux; Secondary: Windows 98SE||Laptop, Sharp Actius, Mobile Pentium II, 300MHz||integrated||integrated|
|PC2002||Primary: Ubuntu 7.04 Linux; Secondary Windows XP Home||PC, Compaq S6000Z, Athlon 2600XP, 1.9GHz||Samsung 170MP, 17” LCD, 1280×1024||integrated|
|PC2006||Primary: Solaris Nevada; Secondary: Windows XP Media||PC, HP a1540n, Athlon 64 x2 4200 dual core, 2.2GHz||Sharp LL193A, 19” LCD, 1280×1024||integrated|
|M2007||Debian Linux||Tablet, Nokia N800, TI OMAP 2420, 330MHz||integrated||integrated|