I borrowed a decent ammeter from work to measure the power usage of
some computers. I am curious which computer is best to use as a home
server running continuously. As others may be interested in how much
their home server is costing them I have posted the numbers below.
The tests were not rigourously controlled but the numbers should be
accurate enough.
The ammeter used is a Fluke 337 "True RMS Clamp Meter." I used an
Extech Line Splitter with a x10 ring for measurements with two
significant digits. Power was calculated as 120V x A. This produces
VA, volt-amps, but most power supplies have decent power factor
correction so true watts should be within +- 10%.
For my use the server will typically be idle or very lightly used. I
made the power measurements when the computers were idle (except one
system). I enabled power saving features and frequency scaling where
available.
Desktops:
97w AMD X2 3800+ 1 GB ram, Seagate 80GB 7200rpm HD, Nvidia 7800GTX
145w Power Mac Dual G4 1.42, 2GB ram, Seagate 320GB 7200rpm + 120GB
7200rpm HD, ATI 9000 video
30w IBM A21, P3 833 MHz, 512MB ram, laptop HD, screen + backlight off
39w as above backlight on full
30w Dell D620, Intel Core Duo 1.83Ghz, 2GB ram, laptop HD, screen +
backlight off
41w as above backlight on full
41w as above no backlight or screen, no cpu scaling, (performance
driver)
52w as above backlight on full, no cpu scaling
39w Dell XPS laptop, Intel Core 2 Duo T7600 2.33GHz, 2 GB ram, 7200
rpm HD, Nv 7900 go
50w as above with screen on
This machine was not at idle when tested.
10w Allied Telesyn 8 port 10/100 switch
10w Linksys WRT54GS
I was surprised by the power usage of the Mac. The G4 was claimed to
be a low power chip but it is 50% worst then the AMD X2. The dual G4
is a 4(?) year old machine. I had expected it to be better then the 1
year old gamer's speced AMD.
The AMD system uses one of the older 89w (TDP) cpus not one of the
newer lower power 65w or 35w cpus. From the spec sheets the 3800+ 89w
and 65w cpus only consume 30-35w when the frequency is scaled to 1Ghz
from 2Ghz. At idle the 35w cpu consumes only 18w. The AMD system is
also sporting a large power hungry Nvidia 7800GTX. If that were
swapped with a lower power card I wonder how much of a difference it
would make.
The laptops are all a little better then I expected. The XPS is a lot
better then expected. The XPS is a "gamer's laptop." With a 17"
screen and high performance parts it is a real boat anchor. Even at
full load it only consumes 90w.
For small home servers old laptops have some advantages. The power
consumption is good. There is a built-in UPS. However performance
suffers, and there is little expandability. Old laptops are often
expensive, but old laptops with broken screens can be found for cheap.
Older hardware is often pressed into service as home servers. It is
readily available and inexpensive. It is often considered to consume
less power then modern cpus. That may have been true two years ago
when the Pentium 4 was warming people's homes. However with the
recent push for more efficient cpus it may be more economical to
carefully build a low power server then scrounge for old parts.
--
sg