Save energy: use Linux

Josip Loncaric josip at
Mon Sep 25 15:43:47 PDT 2000

Jared Hodge wrote:
> We're looking at upgrading our beowulf using the 370DLE, 800EB Mhz
> processors (one per node to start) and 512MB RAM.  If anyone has
> suggestions or warnings, please let me know.

You need at least 300W power supply (350W preferable, with ATX 2.03
auxiliary power connector).  Otherwise, you could draw more than 50% of
peak current rating at +3.3V and +5V rails.  Most power supplies assume
that nominal load is about 50% of peak load.

We've measured our new node AC current requirements today (node = 370DLE
+ dual P3/800EB + 1GB RAM + Giganet cLAN + tulip NIC + 30GB EIDE drive +
floppy + PCI video card).  Here are the results (all AC measurements are
true RMS):

current surge when first plugged in:  2.0  A approx.
current when switched on:             1.02 A max.
current when idle:                    0.66 A typ.
current when normally loaded:         1.0  A typ.
current when VERY heavily loaded:     1.24 A max.
power voltage during test:          123.5  V typ.

Assuming 70% power supply efficiency and assuming that our fans and disk
drives draw about 20W at +12V, I'd say that our units use less than
about 90W of combined +3.3V/+5V power.  For reliability and durability,
you'd want a power supply with about 160-180W combined power rating.  A
300W power supply typically delivers 160W of combined +3.3V/+5V power
(which is probably sufficient), while some 350W units boost this to

BTW, here is the amusing bit of information which prompted the subject
line change: Linux is more power efficient than Windows!  On my loaded
dual CPU box, Linux draws 0.74 A at idle, but Windows NT 4.0 requires
1.14 A at idle.  This means that you can save about 48 W of electricity
by switching to Linux....  Perhaps Linux should get the 'Energy Star'


P.S.  I know, V*A is not W, but W <= V*A when RMS measurements are
used.  We were concerned with upper limits anyway... 

Dr. Josip Loncaric, Senior Staff Scientist        mailto:josip at
ICASE, Mail Stop 132C           PGP key at
NASA Langley Research Center             mailto:j.loncaric at
Hampton, VA 23681-2199, USA    Tel. +1 757 864-2192  Fax +1 757 864-6134

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