Correct me if I'm wrong, but isn't it worse than that. Doesn't the smartphone (or cel
phone) radiate even when you're not talking, so that the system knows where you are if
someone calls you? The only improvement in efficiency I could suggest is electronically
steerable antennae to reduce the required radiated power.
Brent
On 9/20/2013 8:08 PM, L.W. Sterritt wrote:
Chris, Brent and meekerdb,
While we have been considering optimizing the efficiency of circuitry and software, we
neglected that while talking on the smartphone, 1/2 of the total power budget goes to
radiation from the smartphone antenna - about 2 Watts as I remember. That will drain a
typical smartphone battery in less than 3 hours, and there is not a lot we can do about
it, except use the phone for all of it's other functions and don't talk too much!
LWSterritt
On Sep 20, 2013, at 5:24 PM, meekerdb <[email protected]
<mailto:[email protected]>> wrote:
On 9/20/2013 4:40 PM, Chris de Morsella wrote:
Current software is very energy efficient -- and on so many levels. I worked
developing code used in the Windows Smartphone and it was during that time that I had
to first think hard about the energy efficiency dimension in computing -- as measured
by useful work done per unit of energy. The engineering management in that group was
constantly harping on the need to produce energy efficient code.
Programmers are deeply engrained with a lot of bad habits -- and not only in terms of
producing energy efficient software. For example most developers will instinctively
grab large chunks of resources -- in order to ensure that their processes are not
starved of resources in some kind of peak scenario. While this may be good for the
application -- when measured by itself -- it is bad for the overall footprint of the
application on the device (bloat) and for the energy requirements that that software
will impose on the hardware. Another example of a common bad practice poorly written
synchronization code (or synchronized containers).
These bad practices (anti-patterns in the jargon) can not only have a huge impact on
performance in peak usage scenarios, but also act to increase the energy requirements
for that software to run.
I think that -- with a lot of programming effort of course (which is why it will never
happen) that the current code base, and not only in the mobile small device space,
where it is clearly important, but in datacenter scale applications and service
(exposed) applications as well -- that the energy efficiency of software has a huge
headroom for improvement. But in order for this to happen there has to first be a
profound cultural change amongst software developers who are being driven by speed to
market, and other draconian economic and marketing imperatives and are producing code
under these types od deadlines and constraints.
There's a lot of bad design in consumer electronics, particularly in user interfaces,
because the pressure is to get more and newer features and apps. Eventually (maybe
already) this will slow down and designers will start to pay more attention to refining
the stuff already there.
If there is a theoretical minimum that derives from the second law of thermodynamics
it must be exceedingly far below what the current practical minimums are for actual
real world computing systems. And I do not see how a minimum can be determined without
reference to the physical medium in which the computing system being measured is
implemented.
It is determined by the temperature of the environment in which entropy must be dumped
in order to execute irreversible operations (like erasing a bit). But you're right
that current practicle minimums are very far above the Landauer limit and so it has not
effect on current design practice. The current practice is limited by heat dissipation
and battery capacity.
In fact how could a switch be implemented without it being implemented in some medium
that contains the switch?
The way to completely avoid Landauer's limit is to make all operations reversible,
never lose any information so that the whole calculation could be reversed. Then
there's no entropy dumped to the environment and Landauer's limit doesn't apply.
Brent
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