Andrew Lentvorski wrote:
kelsey hudson wrote:
Keep in mind that voltage and current are inversely proportionate and
directly relate to how much power the chip consumes: a basic
principle of electronics (Ohm's law) states that voltage equals
current times resistance;
Did you ever wonder why chips are all trying to lower their voltages
given that VI=P and V=IR? It would seem to be a net wash.
*However*, CMOS technologies that we use in modern VLSI chips are, to
a first order approximation, purely capacitive loads (not so true as
we get down to 45nm, but that's for a different day). They behave a
bit differently.
Basically, CMOS gates behave as two switches (one each to Vdd and GND)
which either dump charge onto a capacitive load from Vdd or pull
charge off of a capacitive load and dump it to ground.
If your grind through a bit of (not too hard) mathematics, you wind up
with an interesting result:
P = k C V^2 f where k is a constant of proportionality
Therefore, we have:
Power is linearly proportional to Capacitance
Capacitance is pretty much set by technology and size of chip. Not a
lot you can do.
Power is linearly proportional to Frequency
This is why we don't see a lot of 4GHz chips floating around. They
burn twice as much power as 2GHz and the overhead of trying to run
something that fast eats into the time to do actual work. So you burn
twice the power but don't quite get twice the performance. There is a
"sweet spot" where 60-70% of your on chip logic arrives "just in
time". That pretty much sets your optimally efficient performance and
power.
Power is *quadratically* proportional to Voltage
This is *huge*. If you manage to halve your voltage, you cut your
power to 1/4 of the original consumption. However, running chips at
lower voltages hurts performance in various ways, so, again, there is
a point at which you stop going much lower. For now, the limit
appears to be about .8V. Much lower than that and you have to start
doing some major tricks to keep your performance up.
And now you know ...
-a
I'm enlightened...
Does that mean that battery life benefits *quadratically* proportionally
or some fraction thereof after considering the other power draws? I
think I read that the L-series processors will allow their notebooks to
draw roughly half of the @34W that the T-series processors do...
In another practical related question I have been mulling over...
If the laptop/notebook is a desktop replacement and you anticipate being
wall powered almost all the time and there is a significant price
differential on this basis of this new processor offering, do you just
take the higher power consumption and the lower price...
I'm thinking you do (max out the RAM for virtualization advances also)...
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