On 11 Mar 2001, at 8:59, Martijn wrote:
> > What about running all the extra floating point operations? Is
> > there no significant affect?
>
> There is a significant diference else there would be no options like do
> not run when on battery power
In theory there should be a difference. In practise the difference in
power consumption is small. Somewhere around 10W seems typical.
I put a current meter on the mains lead of my 1.2 GHz Athlon system,
it registered 0.74A. (We have 240V AC mains power here). I stopped
mprime and the change in current draw was barely perceptible.
CPUs designed for mobile use do tend to use more sophisticated
methods of power consumption control, including turning off parts of
the processor like the FPU whilst they're not in use. Also, 10W is a
much greater fraction of the total power consumption of a laptop PC
than it is of a desktop system unit. However, the option to suspend
Prime95/mprime when operating on battery is really there to reduce
the current drawn from the battery, thereby increasing the run time
before battery recharging is neccessary, rather than to reduce mains
power consumption.
> and would the temperature of an idle
> system not be lower than that of a system running mprime/prime95
Yes, but you have to engineer the cooling to cope with the worst
possible case. However many laptops appear to turn on an extra
cooling fan almost immediately a program which makes use of the FPU
starts.
> With some processors power consuption of an idle processor is less than
> 1/10th of a busy processor.
Yes, using tricks like dropping into a "standby" state where the CPU
clock rate is zero. Signalling an interrupt is required to return the
CPU to normal operation. These techniques reduce the CPU's reaction
speed and are rarely found except in low-drain devices designed for
mobile applications.
Regards
Brian Beesley
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