Trying CHUD’s Nap feature on my Power Mac G4 (MDD)

Posted by Pierre Igot in: Macintosh
January 3rd, 2004 • 2:09 am

A few days ago, I read an article at Other World Computing about using Apple’s CHUD (Computer Hardware Understanding Development) software package to activate a hidden feature in my Power Mac G4 (MDD) that would enable my processors to “nap” and thus reduce the computer’s temperature — in the hope that it would reduce the fan noise levels as well.

I decided to give it a try and downloaded and installed CHUD. I also installed Marcel Bresink’s Temperature Monitor, in order to keep an eye on the temperature before and after activating the “napping” feature.

The trouble is, within 1 hour of checking the “Nap” box in the Hardware control pane installed by CHUD, I experienced something that I haven’t experienced in Mac OS X in ages: a complete system freeze. I was busy reorganizing mailboxes in Mail and did experience an application crash at some point before the actual freeze — so I cannot be sure that the freeze was caused by the “napping” feature. But I have a sneaking suspicion that it was.

In any case, I didn’t notice any decrease in temperature or fan noise levels, so I don’t think I’ll be trying to turn “Nap” on again any time soon.

My quest for powerful yet quiet computing continues…

20 Responses to “Trying CHUD’s Nap feature on my Power Mac G4 (MDD)”

  1. Geje says:

    Hi there,
    I do the same on my G4 MDD bi-867.
    the temperature of the CPUs fall as low as 40° (57° before), so nearly no fan activity is heard.

    beside, I do have the same aparent system freeze (GUI+mouse, but activity continue behind).

    Same test on my friend’s same machine (!), CHUD don’t want to activate Nap, nor switch to single CPU mode, it forgets everything when leaving the preference pane !

    Any other testers ?

  2. Pierre Igot says:

    Yan: thanks for the comments. Out of curiosity, which version of CHUD did you install? (The latest is 3.0.4, and I haven’t tried it myself)

    I doubt that Apple puts much effort into ensuring that this works properly. It’s an “unsupported” thing, basically.

  3. YAN says:

    I’ve used the Nap feature on my G4 MDD 1.25DP 10.3.2 and it did noticeably reduce the temperature and the noise level. (My machine is on my desk and when running the fan noise is ridiculously loud. I’ve installed two extra cards and run four HDDs so I expect it to get a bit warmer in the case.)

    However I’ve stopped using Nap mode it as it has led to numerous system anomalies to what was originally a very stable system. The main issue is the system hangs when trying to wake from sleep. Other times system hangs after using CPU intensive tasks such as iDVD and GarageBand. Also noticed that after a while mouse behaviour is erratic, for example clicking on one file in column view leads to 2 or 3 files either side also selected. When I don’t use Nap none of this occurs.

    I read somewhere on another forum that CHUD may only be for G5s but I have not been able to confirm this. Can anyone?

    If Apple could get it working properly I’d be eternally grateful (and happily pay a small sum) to reduce the noise levels


  4. YAN says:

    Pierre: I used 3.0.2, but will download and try 3.0.4 soon.

  5. YAN says:

    For those interested.

    I have updated CHUD to the latest version 3.5 and the system issues I had from waking from sleep and system hangs have disappeared (note: I am still using 10.3.2)

    Now my machine runs reliably and cool and the noise is greatly reduced!


  6. Pierre Igot says:

    Cool. Thanks for the update. I’m going to give 3.5 a try very soon.

  7. YAN says:

    For Pierre and those interested.

    A little after my last post I started getting system hangs again!

    Anyway, from Mac OS Rumors ( I found the following which pretty well describes the problems I’ve encountered and the solution (CHUD 3.5 with OSX10.3.3

    Keith DeLong
    10.3.3 updated and ran flawlessly on my Dual 1.25GHz Mirrored G4. I had read some early reports of Apple’s performance tool CHUD (on the Panther developer CD) allowing older Macs to run quieter and cooler by employing the napping technology used on the G5s.
    CHUD and it’s updates through the recent 3.5 release have all had the unfortunate side effect of a complete loss of keyboard/mouse access when the temp dropped below about 95 degrees on my G4.
    After seeing the tech note of ‘improved USB support’ in 10.3.3, I decided to try napping again after the 10.3.3 update. It’s now working perfectly! For the first time my mirrored G4 is running reliably at 96-98 degrees with a quieter fan speed instead of the constant 130-132 degrees without napping turned on. CHUD 3.5 is available at this ftp site <;.
    After running the CHUD installer, Open the System Preferences, Select the Hardware Preference pane (in the ‘Other’ section), and select the ‘Nap’ checkbox. That’s all it takes. Using Thermographix or Temperature Monitor, I’m seeing dramatic temperature drop and a slightly more pleasant fan sound with no noticeable change in performance.
    This is a major ‘attaboy’ to Apple for supporting their prior generation hardware.


  8. Pierre Igot says:

    OK, so it seems that both 10.3.3 and CHUD 3.5 are required for the thing to work reliably. Let us know if things stay stable for a while!

  9. AssassinOfGates says:

    I run a dual 867 MDD that was overclocked to dual 1GHz through firmware, CHUD 3.5, and OS X 10.3.3. It freezes frequently when it suddenly goes from a CPU intensive state to a idle state (exiting a video game). It also freezes when I let it go idle for a few hours, in the screensaver (not sleeping). I sincerely doubt it has to do w/ the overclock, because it does this on my roommate’s dual 867 MDD. I still use Nap, but only on hot days when it reaches 93 degrees, cuz’ my room has no AC. I’d rather have a freeze than a toasted computer.

  10. Pierre Igot says:

    Well, I tried it on my system and, while I noticed a decrease in the temperature, I didn’t notice any changes in the noise levels. So I don’t think I’ll be taking the chance of experiencing freezes. Thanks for the update.

  11. YAN says:

    Well, I’ve tried 10.3.3 and CHUD 3.5 and the freezing continues when waking from sleep. Hopefully a future update will overcome the problem.


  12. Johan says:

    I have been running several versions of CHUD now and I am pleased to say with 10.3.3 and CHUD 3.5 I have had very few problems.
    IThe only comment I have is when I try to shut down with NAP activated my system sometimes hangs.
    Dual 1G 2Gmem first generation MDD (with Apple kit (new FAN’s new PS) installed.
    Furthermore I have swapped the stock Alu sink for the second generation Copper one,
    this dropped the temp with 5°C
    I also have had freezes in sleep state but they occur seldom and also with no NAP activated.
    Anyway, the temp drop is fenomenal (from 51° C to 36° C) with NAP turned on.
    There is no silencing effect when turning NAP on, in my case the fan’s start even spinning a little faster and they cycle a bit. It could be that after turning on NAP and waiting for the temp to go stable the overal noiselevel goes down.
    When it’s getting hot in the room (+25°C) silencing does take place, that is a fact.

    Bottom line, this CHUD thing does help.

    On the other hand APPLE could have done a better job in selecting the fans for the exchange kit.
    The PAPST fan they supplied is a good quality one but not one of PAPST’s silencest ones.
    The same goes for those in the PS (never did find their supplier, anyone?) they are more silent than the original DELTA whiners but again they could have selected more silent type.
    My conclusions are based on experiencing fanspeed changes for both the PAPST and the PS fans when activating NAP. The fans are not at all running at 12V and are controlled by temp.changes from at least the CPU’s so putting in more silent fans could silence this machine even more be it with or without CHUD and thus NAP.

    Let me know what you think


  13. Pierre Igot says:

    Thanks for the additional information. My room rarely gets hot, so the benefits for me would probably be minimal. I agree that it is disappointing that Apple has failed to use top-quality parts in their top-of-the-line computers. I could understand cutting corners in lower-range machines — but paradoxically, lower-range Macs tend to be much quieter than their more expensive counterparts. I don’t know about you, but if I am going to spend several thousand dollars on a machine, I don’t mind paying a hundred or two more and having the best possible quality in all parts.

  14. Johan says:

    Could not agree more, I’ve not seen a G5 in real life so I cannot comment on those.
    What I did see is that the design is more efficient in heat evacuation. Like so many others said there were maid some mistakes in the final design of the MDD.
    The housing itself I like, some minor changes could do a lot.

  15. Johan says:

    Did some additional measuring today,
    much to my suprise the Papst 120mm and the small one for the optical bays are connected in parallel, even more strange, they are running at 4,7V when the CPU temp is below 57°C???!!!
    This while the Papst fan has a normal operating range starting at 7V up to 14…
    And even then the 120mm case fan is loud (accomp. bij the two 60mm PS screamers)

    With CHUD the temp can go down to 35°C but even then that 4,7V for the fans is maintained.
    Conclusion; the replacing fans are beter than the Delta screamers but are still badly selected and not used to their full efficiency.
    In some of the other publications someone made a drawing of the positioning between the 120mm case fan and the processor heat sink. I could confirm this misalignment, when looking closely only a quarter of the are moved by the fan is blown against the heatsink, the rest goes wandering in the case. It gets even worse, that quarter displaced air is blown only into the lower part of that heatsink, let this then also be the colder part…
    Inefficiiency at its worst.


  16. Matthias Brennwald says:

    I have a Dual-G4 (FW800, MDD) with a Verax kit installed. Together with NAP activated, the machine is now really quiet (not as quiet as a PowerBook, though), and the CPU temperature dropped from 61 deg.C (typical) to about 45 deg. C (typical). However, I had a few hangs with NAP active… I tried the latest CHUD version (4.0) which is better, but at shutdown the machine would always hang. If NAP is switched off before shutting down, everything is fine.

    I wrote two shell scripts to handle NAP on/off. The first one activates NAP at startup / login:

    hwprefs cpu_nap=1

    The second one deactivates NAP at shutdown / logout:

    hwprefs cpu_nap=0

    I used LoginWindow Manager (look at to make these scripts run automatically at login / logout.


  17. Acacio says:

    I arrived to this page Googling for ” Powermac nap” because I used to have hangs after activating he NAP.

    Just did the upgrade to CHUD 4.0.0.b6 and the nap option is gone.
    hwprefs (cli) now says it’s unsupported for this CPU type (PowerMac 2x 1.42Ghz MDD).


  18. Pierre Igot says:

    Acacio: That’s bad news… :-( I was just about to download and install CHUD 4 myself, because my G4 (dual 1.25 GHz MDD) is very noisy these days, due to the relatively hot weather. But your experience has put a damper on that. No point in installing CHUD 4 if the Nap option is gone — and no point in installing CHUD 3.x either due to the freezes.

    Can anyone else confirm that the Nap option is gone for the G4 MDD?

  19. Johan says:

    To Pierre;

    My system will not even install CHUD 4, the installer asks for certain tools to be installed.
    Running 10.3.5 now.

    To Häkon:

    Have you got any Media readers or things like that connected?
    There is a known issue with “deep sleep”
    I think you can fairly say everything that resembles an external disk connected through USB.
    In my case I have the same problems when connected to the original MB USB ports as those when connected to an zdditional Macally PCI Firewire/USB2.0 card.
    When putting the machine to sleep USB connected things can prevent the machine from waking up (in my case a Sandisk 8 in 1 media reader)

    So try to disconnect as much USB eq. as possible and check if the problem persists.

    Mails to support (Sandisk) result in pointless replys as known issue and just unplug when putting to sleep….


  20. Håkon Lerring says:

    I have this problem that i cannot turn the mac to sleep.. Because if i do, the sytem crashes and i can’t see a thing on the screen. I have tried this with and without Chud tools installed, but nothing works.. annyone got a sollution?

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