OT? power reqs of DDR2 chips

[Les]

On Mon, 2007-05-21 at 20:50 -0700, Wolfgang S. Rupprecht wrote:
> Dave Stevens <geek at uniserve.com> writes:
> > I'm building a new box that will use a DDR2 2G reg/ECC chip. I need to 
> > estimate power draw for the system and can't seem to find a reference. Its 
> > Kingston Value Ram, if that matters. The box _will_ run Fedora.
> 
> I hate to give such a non-answer, but the power consumption is so
> highly determined by your usage pattern that you really can't do
> anything but try it and measure using a very low impedance meter.
> When running block-moves you'll probably see around 2watts per
> actively accessed chip.  Fedora just sitting around will consume quite
> a bit less.  The power will probably be dominated by the termination
> resistors of ~150mw per chip, which will be your ultimate lower bound.
> 
> -wolfgang
> -- 
> Wolfgang S. Rupprecht                http://www.wsrcc.com/wolfgang/
> Hints for IPv6 on FC6 http://www.wsrcc.com/wolfgang/fedora/ipv6-tunnel.html
> 
Also the system needs "overhead" for heavy operation  which is current
capability beyond the rms power draw, much like you buy a 100watt stereo
to get better reproduction of the peaks and high frequencies at 10watts
rms output.  Your choice of video, audio, disks, USB loads, and any HID
devices will also have a big impact.  The MB documentation should give
you some guidelines for typical use, then add hardware, and take a good
look at disk requirements just to begin with.  HID devices may/may not
have external supplies.  

    For memory  and processors, the power factor increases with ram
speed, so the access rate will definitely have impact on your loading,
as will the ram path length (the traces act like a dynamic load until
charged), so the longer the path, the higher the duty cycle for
transition current.  compact boards are faster and more efficient, so
you see lots of really tight layout on the fast blades, or really
compact design in shuttle type cases to reduce path length and
associated losses.

Regards,
Les H