G5: Automatic vs. highest performance mode

artifact of the testing method?

The machine runs faster in the Highest Performance setting. In Automatic, the processor clock speed changes with processor load--the processors actually slow down when there is a lighter load.

If so, why would I want to set it on
Automatic (which is the default, and thus presumedly, Apple's suggested setting).

On Automatic, the processors consume a lot less power, and generate far less heat. For most applications--word processing, surfing the Web, and so on--it makes no difference in performance; these are not processor-intensive tasks.

For processor-intensive tasks, running the processors on their highest performance setting results in better CPU performance, at a cost of more electricity consumed and more heat generated.

In automatic mode the CPU clocks down to arround 1.4GHz. It has been a feature of the PPC's since the iBook 366MHz (with firewire) and PB/PM G4 +667MHz

Running it at slower speed for most activities and highest speed for time critical activities is apparently a way to increase the lifetime of your system. (See the Apple Support Discussions boards (G5); there's been a few discussions about this.) Apparently running it full-bore all the time is not so much of a good thing.

HI,

Yea, I have it in my G5 Dual 1.8 and I have it on Auto.

I have noticed that I will be surfing the web and maybe one time it will start to "rev up"

The noise from it will increase, I spoze the fans kick in (9?) and that makes the noise etc.

The thing is I am just using the web, burn a few discs etc no really intensive tasks on this machine.....

Cheers.

I LOVE MY MAC :)

I had always assumed that running my G5 in "Automatic" would result in it "gearing up to full speed" when a processor intensive load was presented to it for an extended period of time (seconds to minutes, tops).

But apparently this isn't the case:

http://docs.info.apple.com/article.html?artnum=86527

states:

"When using professional applications, games with intensive video processing, or other applications that use the microprocessor intensively, the Automatic option in Energy Saver may not provide the best microprocessor performance. If you know you are going to be placing a significant demand on the microprocessor, change your Energy Saver setting to "Highest", as seen in Figure 1."

This seems a bit silly to me - why should *I* have to turn the knob up to "11"... :-)

Has anybody implemented a "click the box for me" mechanism that monitors system load and switches gears appropriately?

Will setting my dual G5 to "Highest" result in more heat/fan noise?

I got one "slow" number, followed by three (or more) fast numbers

Running them manually sequentially always yielded a "slower" number:

G5:~ jim$ java -server Test
333
G5:~ jim$ java -server Test
333
G5:~ jim$ java -server Test
346
G5:~ jim$ java -server Test
360

I really couldn't figure out why this would be...

... but now I can.

It looks to me like "Automatic" mode kicks things into high gear pretty quickly (in a fraction of a
second) when a heavy CPU load is present:

Reduced:

G5:~ jim$ java -server Test;java -server Test;java -server Test;java -server Test
381
381
381
381

Highest:

G5:~ jim$ java -server Test;java -server Test;java -server Test;java -server Test
248
250
249
248

Automatic:

G5:~ jim$ java -server Test;java -server Test;java -server Test;java -server Test
360
248
248
247

Note that after the first 1/3 of a second, Automatic mode ran just as fast as "Highest" mode. The fact that the benchmark test executes in almost the same time that it takes for the G5 to "kick into high gear" was just a "lucky" coincidence.

Just to be sure, I changed the inner loop by a factor of 4X:

G5:~ jim$ #Auto
G5:~ jim$ java -server Test4;java -server Test4;java -server Test4;java -server Test4
1049
974
971
972
G5:~ jim$ #Highest
G5:~ jim$ java -server Test4;java -server Test4;java -server Test4;java -server Test4
973
974
976
972
G5:~ jim$ #Reduced
G5:~ jim$ java -server Test4;java -server Test4;java -server Test4;java -server Test4
1492
1493
1496
1497

Based on these numbers, I'd say that it takes somewhere between 0.2 and 0.35 seconds to get up to speed when running in automatic mode. After that, your CPU is running just as fast as if you had set it for "Fastest".

The good news is - automatic should be fine for most all purposes on a G5. There is no performance penalty when doing long-running CPU intensive things like DVD rendering, MP3 encoding, etc.

The bad news is - I don't get a speed boost by simply clicking a pop-up menu... :-)

If anyone has any evidence of "Automatic" seriously compromising a G5's performance, please follow-up. But for now, I'm leaving my G5 on "Auto"...