[mythtv-users] CPU power (was Possible small HD frontend)

[Brian Wood]

On Mar 22, 2008, at 8:25 AM, Brian Phillips wrote:
>
> Seems logical as the power consumption for an idle transistor is very
> minimal, if completely unnoticeable.  Transistors use the bulk of  
> power when
> they need to make a state change.  The clock speed only affects the  
> clock
> signal, which is a minute number of transistors when you compare it  
> to the
> cache on chip, ISA transistors, etc.  If you clock the chip slower,  
> you
> aren't saving any noticeable amount of power because you are only  
> reducing
> the number of state changes in the clock generation and processing
> transistors.
>
> If you are actually processing something, you are changing the state  
> of the
> majority of transistors on the chip and therefore you will see the  
> most
> power usage.  By slowing the clock, you aren't saving anything.  The  
> total
> amount of power needs to be spent to process your instructions, you  
> are just
> lengthening the time over which those instructions are processed.   
> You might
> see lower instantaneous power usage, but summed over time you will  
> see very
> little difference in power usage.
>
> This is all assuming minimal power lost to generation of heat, which  
> AMD is
> losing the battle on due to trying to keep up with Intel's  
> technology.  Or
> so I hear.

So slowing the clock is just a thermal issue? The same amount of work  
over a longer time would require heat to be removed at a slower rate,  
thus allowing slower fans?

Slowing the clock is certainly touted as "green" in a lot of circles,  
but it wouldn't surprise me if it is marketing and not engineering. I  
seriously doubt the power saved by slowing the fan(s) would be  
significant.

beww