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Up to Discussions in Portable Macs
15 Replies Last post: May 20, 2006 9:16 PM by macnuke   1 2 Previous Next
Click to view Typhoon14's profile Old Hand
Typhoon14
2,156 posts since
Feb 2, 2001
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May 20, 2006 5:06 PM

Explanation of Processor Speed Settings

Does anyone know exactly how the "automatic" setting for CPU speed works on PowerBooks and other Macs? I had always assumed the automatic setting would give you ideal power usage without a performance hit by cutting CPU speed during low usage, and raising it when needed. Recently, however, I happened to switch it to "highest" on my PowerBook G4 while playing with settings, and was amazed at the speed difference. For example, ripping a DVD to MPEG4 with CPU speed set to Auto goes at a rate of around 18 frames/sec. Set the CPU speed to "highest" and the rate instantly shoots up to around 33 frames/sec.

I'm hoping someone can shed some light on what criteria the system uses for choosing the CPU speed automatically, or whether the CPU simply does not switch to full-performance while on automatic.
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Click to view macnuke's profile Old Hand
macnuke
6,672 posts since
Mar 5, 2004
1. May 20, 2006 5:31 PM in response to: Typhoon14
Re: Explanation of Processor Speed Settings
it's my understanding that automatic lowers power consumption by regulating thruput.
lowering processor speed and bus speed to save the power.
if the processor can do the same task slower with less energy used, it will.
in other words, our 2Ghz isn't running at 2Ghz.
power = speed in this instance.
less power, less heat, less energy loss thru that heat as well.

that's the closest explanation I could ever get on the energy settings.
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Click to view Typhoon14's profile Old Hand
Typhoon14
2,156 posts since
Feb 2, 2001
2. May 20, 2006 6:31 PM in response to: macnuke
Re: Explanation of Processor Speed Settings
Ah, but I'm still curious as to what sort of activity causes the processor to switch into higher gear. I would think that having the CPU pegged at reduced speed would induce the system to increase CPU speed, but this does not appear to be the case.
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Click to view Typhoon14's profile Old Hand
Typhoon14
2,156 posts since
Feb 2, 2001
3. May 20, 2006 6:42 PM in response to: macnuke
Re: Explanation of Processor Speed Settings
Hm, I did a little reading on the Apple forums. It appears that newer Macs lack the user CPU control option (Last PowerBook revision and the MacBooks). Can anyone confirm whether the "Processor performance" setting is available in energy saver options on these models?
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Click to view iDaver's profile Member
iDaver
315 posts since
Jun 3, 2001
4. May 20, 2006 7:01 PM in response to: Typhoon14
Re: Explanation of Processor Speed Settings
The processor performance setting is not available on my MacBook. There are settings for "better battery life," "normal" or "better performance." It's not perfectly clear what these settings affect except that "better battery life" automatically changes the sleep time settings when chosen.
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Click to view macnuke's profile Old Hand
macnuke
6,672 posts since
Mar 5, 2004
5. May 20, 2006 7:42 PM in response to: iDaver
Re: Explanation of Processor Speed Settings
changing the sleep time won't give you better battery life if you are using the computer during the life of the battery... in other words, something else has power cut to it to increase the battery life.
the only other thing that would improve battery life would be less heat, which is less power which is lower performance.
in other words... a reduced clock
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Click to view Typhoon14's profile Old Hand
Typhoon14
2,156 posts since
Feb 2, 2001
6. May 20, 2006 7:42 PM in response to: iDaver
Re: Explanation of Processor Speed Settings
Even in the extended "Options" section of Energy Saver? - http://www.celestialfrontiers.com/images/temp/cpu.jpg
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Click to view macnuke's profile Old Hand
macnuke
6,672 posts since
Mar 5, 2004
7. May 20, 2006 7:48 PM in response to: Typhoon14
Re: Explanation of Processor Speed Settings
some of the items better battery life gives you also is this...

On PowerBooks and iBooks:
The Ethernet port turns off (see Note below)
Expansion card slots (such as PCMCIA) turn off
The built-in modem turns off (see Note below)
An AirPort card, if present, turns off (see Note below)
The ADB or USB connection only responds to the power key on an external keyboard (see Tip below)
The optical media drive spins down
Audio input and output turns off
Keyboard illumination, if a feature of your portable computer, turns off.

it still doesn't discuss the processor performance that Typhoon originally asked tho.
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Click to view Typhoon14's profile Old Hand
Typhoon14
2,156 posts since
Feb 2, 2001
8. May 20, 2006 7:52 PM in response to: macnuke
Re: Explanation of Processor Speed Settings
Where'd you get that list from? I often use Better Battery Life on-the-go, and none of those system functions are deactivated. Indeed, if they were, the machine would be pretty useless in that mode.
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Click to view iDaver's profile Member
iDaver
315 posts since
Jun 3, 2001
9. May 20, 2006 7:54 PM in response to: Typhoon14
Re: Explanation of Processor Speed Settings
In reply to:<hr />
Even in the extended "Options" section of Energy Saver?

<hr />

No, not on the MacBook.
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Click to view macnuke's profile Old Hand
macnuke
6,672 posts since
Mar 5, 2004
10. May 20, 2006 7:55 PM in response to: Typhoon14
Re: Explanation of Processor Speed Settings
heh
sorry, the note got cut off. poor cut and paste on my part..

if any of the items listed are in use, stay that way.. if they are idle, then the de-activation occurs.
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Click to view Typhoon14's profile Old Hand
Typhoon14
2,156 posts since
Feb 2, 2001
11. May 20, 2006 8:03 PM in response to: macnuke
Re: Explanation of Processor Speed Settings
Ah . . .

I'm rather confused as to why that wouldn't be the case with all the power settings. After all, what's the use of powering devices when they are not being utilised?
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Click to view Typhoon14's profile Old Hand
Typhoon14
2,156 posts since
Feb 2, 2001
12. May 20, 2006 8:04 PM in response to: iDaver
Re: Explanation of Processor Speed Settings
In reply to:<hr />

No, not on the MacBook.


<hr />

Nice to know. Hopefully, the auto-CPU-adjustment functionality works better on the MacBooks.
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Click to view macnuke's profile Old Hand
macnuke
6,672 posts since
Mar 5, 2004
13. May 20, 2006 8:19 PM in response to: Typhoon14
Re: Explanation of Processor Speed Settings
like everything else that is turned on and off with a soft switch, leaving it on makes it more reliable.
yes, it does make sense to power things down that you aren't using, but it isn't always that easy.

get bored, run xbench with each of the settings.
it's not a matter of just turning off unused stuff.
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Click to view MacCheetah3's profile Old Hand
MacCheetah3
6,635 posts since
Apr 2, 2001
14. May 20, 2006 8:36 PM in response to: macnuke
Re: Explanation of Processor Speed Settings
Hi
This was an argument when the Processor Performance option was first implemented. It seems, Automatic is much closer to Lowest and has been noted not to respond and change frequencies quickly at all.

I can't find the article where Apple explicitly claims to use Highest if you are using a desktop i.e. Power Mac G5. Anywho...

Apple Knowledge Base Article #86612 - About Automatic Processor Performance Setting

Apple MacBook (Black) 2.16GHz C2D, 4GB, 200GB (7.2K), DL-SD + 16GB iPod touch - Debug Computer Services http://www.click2debug.com
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