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

[Phil Bridges]

On Sat, Mar 22, 2008 at 10:31 AM, Brian Wood <beww at beww.org> wrote:
>
>
>  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
>

Doesn't it also use fewer W from the power supply?