The machine will not boot without both of them physically installed.

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That is strange, as I have a damaged Dual 2.5GHz G5 PowerMac that only reports one of the two installed G5 CPU's as working, and when I swap them for each other, it still reports the same unit number as working. So, this leads me to believe that the fault is with the motherboard, not either of the G5 CPU modules. It has no problem in booting MacOSX with just the one G5 CPU module being reported as working, so I wonder why the PowerMac won't boot if one of the two G5's is removed from the system?

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Have you tried resetting the nvram?

Hold Cmd-Opt-P-R and power on, keep the keys held down until you hear the boot chime for the second time.

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In the Apple developer tools there was a thing called CHUD tools processor pref pane that let you disable a CPU in a dual machine.
You can also do it through terminal. I don't recall if it survived reboots. If you dual boot, it might be worth taking a look.

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Thanks, I'll look into it and report back.

Hmmm.... Maybe with one removed it will boot then. I just seemed to remember attempting it when my 2.5 G5 killed a CPU from a cooling leak. Give it a try, Im curious now.

I remember someone told that if you remove one CPU the system fans will run 100% all the time. If you try, let us know if this is true or not.

Any news on this topic?

> Any news on this topic?

Seems Intuition's suspicion in posting #5 was correct:

https://morph.zone/modules/newbb_plus/viewtopic.php?topic_id=11055&forum=11&start=23

I tried the OF lines on post #1. My system works fine (I think) but I can't really tell the difference.

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In other words: setting cpus to 1 in OF ist just a hint for the OS. It's up to the OS to actually deactivate one CPU. Thus, wenn booting MOS, both CPUs will bi active then...?

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Has anyone confirmed that this actually lowers power consumption when running MorphOS on a dual G5 PowerMac? I read in another thread that even though the 2nd CPU can be disabled for use by the OS and software, it does not prevent it from using the same amount of electricity, or producing heat.

If it actually can be turned off and saves electricity and heat production, I will definitely use these commands on my dual 2.7GHz G5. I am not sure how to test this, and don't have an amp meter to check the amount of power being used before and after these commands are executed to run MorphOS.

Even without the 2nd G5 CPU disabled using these commands, I wonder if both G5's ramp up to the same operating speed, when any MorphOS software demands more computing power from the one G5 CPU it is accessing? I would guess that the 2nd G5 remains at an idle speed constantly while running MorphOS, but again, I have no way to test and confirm this guess.

> Has anyone confirmed that this actually lowers power consumption when running MorphOS
> on a dual G5 PowerMac?

No.

> I wonder if both G5's ramp up to the same operating speed, when any MorphOS software
> demands more computing power from the one G5 CPU it is accessing? I would guess
> that the 2nd G5 remains at an idle speed constantly while running MorphOS

Both G5 CPUs remain at maximum clock speed constantly while running MorphOS.

I tested it long time ago (along with PB G4) and the power draw was the same as with 2 CPUs. I stored data results somewhere but can't find it atm. I can do the tests again someday if needed.

[ Edited by Korni 29.08.2015 - 18:53 ]

I think i will stick with a single cpu g5

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No need to test again, I trust your results from the first test you did.

> [...] it's possible (now or at a future date) to disable the 2nd CPU in MorphOS?

"Disabled the second CPU on PowerMac7 machines"
http://www.morphos-team.net/releasenotes/3.10

Will it be possible to physically remove the one cpu and boot straight into MorphOS by disable the one cpu? Or both should be installed and one gets deactivated after you boot into MorphOS?

+1

I test to disable second CPU.. but not effect....

Any idea ?
thanks

Have You checked power consumption or temperature inside Your G5?

i show 2 CPU in task manager.

Temperature : 84 - 86 C ....

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Doesn't 3.10 disable the second cpu?
That should reduce temperatures.

On my G5 (2.3GHz) it probably does: CPU1: 75°C, CPU2: 52°C ! Under MOS 3.9 both CPUs had about 72°-76°C

You can get a plug in wattage tester for less than 10 euro these days. Always handy for diagnosing issues with equipment.

I suspect though that disabling one G5 won't result in drastic difference in power consumption, if it's still idling at ~50C. But still, it's something.

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Almost 5 years later, I finally made time to test my faulty dual 2.5GHz G5 PowerMac, with one of the two G5 CPU's removed from the system completely. It does not boot, or even appear to attempt the boot process.

During this removal for testing, I did find what is wrong with my dual 2.5GHz G5 PowerMac, which prevents one of the two confirmed working G5 CPU's from showing up as working.(I have swapped them, and the same G5 unit numbers report working and non-working, when the G5 CPU modules are swapped) The motherboard socket for the upper G5 CPU has 2 or 3 pins that appear to have been bent over and perhaps burned away due to a short circuit, or broken off, due to multiple installation and removal attempts.

Once I obtain some new "O"rings and replacement coolant liquid, I plan to re-assemble this dual 2.5GHz G5 PowerMac, install a demo copy of latest version of MorphOS available at that time, and then give it away as a raffle prize at this year's AmiWest Show. Since only one of the G5 CPU's is working and it is not worth the effort of trying to repair/replace the faulty G5 CPU socket, this G5 is only good for running MorphOS alone, and much less useful as a dual boot system, with any other OS which is SMP capable.