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Check CPU speed settings on iMac G5s System
I am not sure if this has been posted yet, but you can speed up your iMac G5 by doing the following. Open System Preferences, and navigate to Energy Saver -> Options -> Processor Options, and set it to Highest.

If it is set to Automatic, the G5 ratchets the processor down like a laptop; i.e. when you are not doing anything strenuous, the processor does not perform at its highest level. It is supposed to kick into high gear when the system detects a heavy load, but does not seem to do so adequately. When playing the Battlefield 1942 demo on automatic mode, I could barely play it at 640 x 480 lowest graphics mode. Once I set the processor to Highest, I could then play smoothly at 800 x 600 with medium graphics. One caveat, it yet has to be seen how this will affect the life of your processor.

[robg adds: We discussed this before relative to new PowerBooks .... it seems at least some new desktops are also set to Automatic out of the box.]
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Check CPU speed settings on iMac G5s
Authored by: Anonymous on Nov 17, '04 09:50:28AM

Does choosing this setting impact the fans at all? Does running full-bore all the time make cause the fans to run faster/more often? This could be an issue if increased noise is a concern...



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Check CPU speed settings on iMac G5s
Authored by: greed on Nov 17, '04 10:29:32AM

I can't say for certain, but I would expect that the CPU is still "halted" while idle. So the system clock remains at high-speed, but if the system runs out of tasks which need to run, it will stop the CPU until something happens (timer expires, I/O completes, that sort of thing). When stopped, it will use a fraction of the power as compared to when it is executing instructions. And power is heat on a chip--it isn't turning into anything else.

So, combined with thermostatic fan controls, the fans should only come up to top speed if you're running a CPU-intense job, like video rendering or conversion, a big compile job, or some serious number-crunching.



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Check CPU speed settings on iMac G5s
Authored by: macgruder on Nov 17, '04 10:28:26AM

There is some note on the discussions area of Apple.com that this can cause your G5 to crash though. I have a G5 iMac, and sometimes I would come back to the computer after being away for a few hours and it had completely crashed. Fans on full bore, no screen image whatsoever, and the only way to restart would be to hold down the power button for a few seconds. Since changing back to auto I don't have those problems, but it's too soon to make a true assessment. Perhaps other people could report back if they have the same problmes.



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Check CPU speed settings on iMac G5s
Authored by: Finney on Nov 17, '04 11:46:09AM

I leave my iMac G5 (20"/2GB) set to highest all the time. I leave my iMac on virtually 24/7 and I have yet to have any freezes/crashes. The fans are slightly louder when it is set to highest, but for the most part I can't tell any difference, except for the fact that my Mac is so incredibly fast I don't know what to do with myself!



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Check CPU speed settings on iMac G5s
Authored by: raider on Nov 17, '04 11:50:50AM
It might be worth noting, that doing this on a PowerBook 15" 1.5Ghz causes a loud buzzing noise:See this thread on the Apple Discussions.

This is from one of my postings on that topic. Anyone know where I can find some info about CHUD tools? I have XCode already installed and I can't seem to find out...

I did some performance testing and found this:

I ran XBench processor benchmarks, and the numbers showed a huge difference (higher is better):

Reduced: 91.94 Automatic: 96.47 Highest: 183.31

I ran the benchmarks several times, and got consistant results. According to this, it would seem there was almost a 100% difference in processor performance.

I ran the "Altivec Fractal Carbon" benchmark, using single processor settings and 131k maximum colors (smaller time and higher MFLOPS is better):

Reduced: 121.8 seconds - 3192.9 MFLOPS Automatic: 60.6 seconds - 6413.1 MFLOPS Highest: 60.3 seconds - 6452.1 MFLOPS

I did a "real world" test using Eclipse 3.0, and Tomcat. Using Eclipse to start my development apps in Tomcat (lower is better):

Reduced: 19000ms Auto: 11000ms Highest: 11000ms

I ran this test several times each to make sure that caching was not effecting too much, and results were consistant. I am not sure how "processor constrained" this process is, but you can see that comparing "reduced" to other settings - there is an impact.

So based on my comparison, one benchmark says there is a pronounced difference between "Automatic" and "Highest" but another and real world performance seems to say otherwise. I don't know what the official answer is, but it looks as though the performance difference in real use is negligible - but the noise difference is wonderful. :)

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Check CPU speed settings on iMac G5s
Authored by: Timbuk3 on Nov 17, '04 09:06:53PM

CHUD is not installed by default with developer tools. It's an extra package you have to select.



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Check CPU speed settings on iMac G5s
Authored by: stev0621 on Nov 18, '04 07:29:48AM

Check out page 38 of MacAddict's December Mag for some real-world benchmarks. The Proc set to highest wins in almost every catagory; over qautomatic. It is also interesting to note the comparison to a 1.8Ghz PowerMac G5.

---
"God set definite bounds on man's wisdom,
but put no limits on his stupidity."



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Check CPU speed settings on iMac G5s
Authored by: raider on Nov 18, '04 09:27:57AM
Well, I don't have the magazine in front of me (I'll have to check it out when I can) and they don't have their articles on their website. But in their forums, they have a thread discussing the article, and one of the posters had about the same experience as mine when they tested their machine. Check out this post.

Your mileage may vary. But all I know is that my Powerbook makes a VERY ANNOYING noise when set to "Highest" so I keep it at "Automatic" for my own sanity, and I have not noticed a difference in my usage. And I use my PowerBook 15 hours a day. :)

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Check CPU speed settings on iMac G5s
Authored by: stev0621 on Nov 18, '04 11:04:20AM

I haven't really run any benchmarks per se, myself. My experience has been that it does not "feel" any faster during normal operation; ie word, photoshop, iTunes. However, as I posted in the original thread, when running Battlefield 1942 it runs dog slow at 640 x 480 when set to automatic. Setting it to highest yeilds much better performance. Nanosaur 2 does not show any difference. My guess is that some programs and games don't cause the processor to ratchet up like it should. There is no doubt that the fans run louder, though; as they should with the proc running hotter.

---
"God set definite bounds on man's wisdom,
but put no limits on his stupidity."



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