Processor performance: automatic vs reduced


I have a 12" powerbook, on which I mainly do software development. I frequently use a lot of CPU time doing processor intensive tasks like compiling code, etc and want to get as much battery life as possible out of my machine, even if it runs a bit more slowly. To this end, I decided to set my Processor Performance in the Energy section of system preferences to Reduced instead of Automatic. It might just be me, but it seems like the power doesn't drain any more slowly than it does when set to Automatic.

Does anyone know if this really does make a difference? Can the machine save even more power under certain circumstances when in Automatic mode or something?


Staff member
Hm. Haven't given it much thought, really. Put it to automatic for my PB, and it was good for me...


In Geostationary Orbit
My guess is when Automatic is on the Energy Saver senses when the Powerbook is on battery or on the A/C. When on the battery in goes to reduced mode. When the Powerbook is on the A/C the Energy Saver speeds up the processor speed.

Warning: This is only a guess.


I'm not sure it works that way. There's a seperate setting for battery and power adapter mode, so you can have the two modes on either Automatic, Highest or Reduced seperately depending on whether or not you're plugged in.

My guess is that Automatic runs the proc faster or slower depending on what kind of things are running -- for CPU intensive activities it would run faster and take more juice but if you're doing mostly user-interface stuff like web browsing or typing a paper (or if the machine is idling) it'll take less power.

My question is whether the Reduced setting actually saves the most power or whether the automatic throttling can possibly consume even less power depending on activities. Anyone know?


Registered Bot
Reduced lowers the clockspeed.

So does automatiic. . . uh, automatically.

I would assume Reduced would use the absolute lowest possible power. And Automatic is a nice compromise.

Having said that, you may just have to benchmark both ways.



Digital Music Pimp
um. i think lowest goes to "low". automatic changes dynamically based on load, does it not?