Exclusive: ZDNet overclocking tool enhances performance of Mac Pro

Why does ZDNet Clock run on Mac Pro computers only?
Different models use different clock chips. These chips must be programmed in a totally different manner. ZDNet started with Mac Pro since they are the preferred computers of users who demand maximum power. Feedback from our readers shows us that there is much interest in support for more models.

MacBook owners should be aware that they will not achieve a great performance increase when overclocking. Running a notebook computer under full load will push the temperature to the limit after a couple of minutes, even if not overclocked. This causes the CPU to throttle. Overclocking a notebook computer results in better performance for a few minutes only.

Is there a chance that my computer will not boot after running ZDNet clock?
No, ZDNet Clock does not load a kernel extension (kext) at boot time. After powering off, the system boots at stock speed.

Will ZDNet Clock shorten my computer’s life?
Hardly at all, since ZDNet Clock does not increase the voltage. We estimate that the computer’s life expectancy may be shortended from 20 years to 19.5 years. Core 2-based CPUs at stock speed run well below their theoretical limits, and one can generally expect a long lifespan.

Are there any risks involved in overclocking by a great deal?
As with any system crash, you lose unsaved files. Since HFS+ is a pretty robust filesystem, it recovers well at the next reboot.

Benchmarks, for example XBench, Cinebench and Geekbench, do not run faster after overclocking.
Yes, they do. As stated on page 3, Mac OS X uses the bus clock as a real time source. This causes the system clock to run faster, so benchmarks will show the same results as without overclocking. Use a stopwatch to see the performance increase.

Why does the system clock run faster? Is there anything I can do?
This is due to the fact that Apple adjusts the real time clock to bus clock ratio at boot time only. On newer Mac Pros (early 2008), simply do a warm reboot. There is currently no solution for older Mac Pros.

Apple did something wrong? This is impossible.
If you use the bus clock as a real time source, this works as long you do not change the bus clock’s speed. However, especially on notebooks, the bus clock does not run at constant speed, even without overclocking. Under full load, upon reaching a certain threshold temperature, notebook processors will leave out bus cycles to cool down. This leads to known problems with USB and Firewire audio devices. Audio playback may start stuttering. The same problems occur when you overclock a Mac Pro.

On notebook computers, the problem disappears when then computer runs idle for a while and has some time to cool down. On a Mac Pro, you have to revert to stock speed. An acceptable workaround is to overclock only when you specifically benefit from it, for instance while encoding or rendering.

If you read between the lines of some of the answers in the Apple developer support forum, you will realize that Apple is obviously aware of these problems. There seem to be some integration issues between the Mach part and the BSD part of the kernel. Most likely, they are working on it.

My system crashes when I overclock by only 5 MHz. What is the cause?
Overclocking means a speed increase of the CPU, front side bus and main memory. All those components must be able to operate safely at a higher speed. If Apple install a CPU specified to run at 2.80 GHz, they cannot be blamed if it does not run at 2.81 GHz.

In ZDNet’s experience, RAM is the most likely component to fail when overclocking. Pre-installed Apple memory is generally of very good quality. Cheaper RAM from Transcend or Kingston performs even better. Many other brands, however, do not meet ZDNet’s expectations. Corsair even refused to supply ZDNet with samples. They state that their memory modules are not designed for overclocking.

One should also be aware that Transcend, Kingston, Corsair, OWC, iRAM and CSX are just brand names. These companies get supplies from a variety of sources. Quality may vary from batch to batch.

Themenseiten: Mac

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36 Kommentare zu Exclusive: ZDNet overclocking tool enhances performance of Mac Pro

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  • Am 29. Juni 2008 um 7:09 von Matthew

    Underclocken fuers MacBook
    Auch wuenchenswert waere die Moeglichkeit einen Processor zu underclocken. Die MacBook Pros naemlich laufen sehr warm (deshalb auch sehr laut) unter voller Belastung. Optimal waere wenn der underclockte Rechner eine grosse Aufgabe langsam waehrend der Nacht bearbeiten koennte, ohne dass der Ventilator sich kaputt spinnt.

  • Am 30. Juni 2008 um 15:47 von Gerry Conway

    Unable to download – no file in ftp://ftp.zdnet.de/pcpro/download/swlib/08/ZDNet_Clock.tar.bz2/ directory.
    There is no file in this directory for download.

  • Am 1. Juli 2008 um 12:51 von Arne

    I cant download!

  • Am 1. Juli 2008 um 14:50 von James K. Boodley

    Overclock nicht arbeit mit Mac Pro 3.1
    (nur ein bicien Deutch)

    Ich habe ein MacPro mit 2 x 2.8GHz quad-core Intel Xeon (model 3.1), 4GB RAM, und OS 10.5.3. Overclock nicht arbeit: "You can’t open the application ‚ZDNet Clock.app" because it is not supported on this architecture." Was ist loss?

    Hilfe, bitte. Vielen dank!

    (My high school German is rusty so here’s the English version:)

    I have an eight-core Mac Pro with two 2.8GHz Intel Xeon quad-core processors, 4GB RAM, running OSX 10.5.3. When I try to run Clock, I get the error message "You can’t open the application ‚ZDNet Clock.app" because it is not supported on this architecture." I’ve tried removing the non-Apple RAM I have installed but still get the same message.

    Any help would be appreciated. Thanks!

    Kind regards,

    James Boodley
    (Ithaca, New York, USA)

    • Am 15. Dezember 2016 um 0:02 von mario


      did you solved this problem with ZDnet overclocking because i have the same problem/error message.

      It would be nice if you have the answer for me to solve this problem.

      please let me know if you have.

      best regards,


  • Am 3. Juli 2008 um 16:43 von Matt

    Faster time
    Something to keep in mind when using this, your system clock is going to run fast. That is your time clock will get ahead of itself proportionally to the amount you’ve overclocked your mac pro.

    Just keep it in mind :)

  • Am 3. Juli 2008 um 23:44 von Samos

    OK 2 or 3 times, suddenly won’t work anymore…
    … since I made the "kextunload -b de.zdnet.kext.overclock" trick in a root user terminal. ??? …

    Is there any reverse action ?

    It worked great before, on MP 3,1, I’m disappointed

  • Am 7. Juli 2008 um 11:22 von Per S Jørgensen

    Computer: MacPro 2.1 Crashes
    Can`t take the bus clock to more than 340 MHz before it crashes that`s only 7 MHz up
    ; (

    • Am 11. Juli 2008 um 10:36 von ZDNet

      Bad Ram=Bad Overclocking
      As mentioned in the article, oc depends on the memory-modules. A lot of users do have problems with RAM from OCW when they try to overclock their Mac pro. Apple-Ram is ok for oc. Modules from Transcend and Kingston are even better.

  • Am 9. Juli 2008 um 23:37 von BDJ

    This screws the system clock
    Overclocking my MacPro results in my system clock running too fast. At the end of one day my clock will be 20 minutes ahead.

    • Am 11. Juli 2008 um 10:49 von ZDNet

      Try to reboot
      If you have a MacPro3.1 (2008-Model) you can reboot to get the clock running correct. For earlier version of mac pro there is right now no solution.

  • Am 14. Februar 2009 um 17:34 von dave

    time fix
    if people are worried about the system clock getting out of sync, just run this in the terminal:

    sudo ntpdate -u

    If you download Lingon and make a launchdaemon, you can have it do it automatically every x minutes.

    • Am 28. November 2009 um 21:05 von JUN

      AW: time fix

  • Am 29. April 2009 um 12:00 von Cmyk

    Funktioniert nicht mit MacPro Quadcores (Nehalem)

  • Am 3. Juni 2009 um 21:31 von Mariano

    Mac Pro 3.2 Overclocked at 3.6 working perfect!
    I overclocked my mac pro 2008 generation at 3.6 and works perfect. I will keep trying more, but my question is how to keep the computer overclocked after shoot it down. I mean, do I have to overclock the computer after each time that I turn it off? There is any way to make a permanent overclock?
    Any way,
    Thanks for this tool!

    • Am 5. September 2009 um 23:41 von Enrique

      AW: Mac Pro 3.2 Overclocked at 3.6 working perfect!
      It worked fine until I upgraded to Snow Leopard.
      Now it tells me that it’s not compatible with OS.

      • Am 7. September 2009 um 11:42 von Cyrano

        AW: AW: Mac Pro 3.2 Overclocked at 3.6 working perfect!
        try with kernel 32 bits and after reboot on kernel 64 bits

        • Am 8. September 2009 um 2:24 von peanutplanters

          AW: AW: AW: Mac Pro 3.2 Overclocked at 3.6 working perfect!
          I cant get this to run on Snow Leopard either… any plans for an updated version? Or a work-around for the version check?

          • Am 10. September 2009 um 16:33 von Cyrano

            AW: AW: AW: AW: Mac Pro 3.2 Overclocked at 3.6 working perfect!
            start on leopard
            overclock your computer
            re-boot on snow leopard

            for me start on snow leopard 32bits (default)
            overclock my computer
            re-boot on snow leopard 64 bits (keys 6+4)

          • Am 12. September 2009 um 20:27 von peanutplanters

            AW: AW: AW: AW: AW: Mac Pro 3.2 Overclocked at 3.6 working perfect!
            Boot into Leopard? That’s not possible once you’ve upgraded to snow leopard. And the overclock only lasts until your computer gets powered down.

          • Am 14. September 2009 um 13:10 von Tails

            AW: AW: AW: AW: AW: AW: Mac Pro 3.2 Overclocked at 3.6 working perfect!
            It is possible. The overclock resets only if you shutdown your mac, not if you restart it. Just boot into Leopard, overclock it and then restart it through Snow Leopard.

            I use it that way and it works. Although I have encountered some kernel panics on Snow Leopard at overclock speeds which didn’t give me any trouble through Leopard before. So you’ll probably need to do the tests again if the machine is stable through snow leopard.

          • Am 17. September 2009 um 21:32 von xgman

            AW: AW: AW: AW: AW: AW: AW: Mac Pro 3.2 Overclocked at 3.6 working perfect!
            Anyone know how to request the author of this take a look at 10.6?

          • Am 18. September 2009 um 1:44 von xgman

            AW: AW: AW: AW: AW: AW: AW: AW: Mac Pro 3.2 Overclocked at 3.6 working perfect!
            Actually, never mind it works fine in Snow Leopard, at least in 32 bit mode.

          • Am 30. September 2009 um 18:20 von peanutplanters

            AW: AW: AW: AW: AW: AW: AW: Mac Pro 3.2 Overclocked at 3.6 working perfect!
            Please explain how you boot into Leopard after upgrading to Snow Leopard? Unless you have 2 separate installs.

          • Am 30. September 2009 um 18:21 von peanutplanters

            AW: AW: AW: AW: AW: AW: AW: AW: Mac Pro 3.2 Overclocked at 3.6 working perfect!
            And xgman, how did you get it running in 32-bit snowleopard? When the application runs, it clearly states that it only supports 10.5.x

          • Am 4. November 2009 um 3:17 von peanutplanters

            AW: AW: AW: AW: AW: AW: AW: AW: AW: Mac Pro 3.2 Overclocked at 3.6 working perfect!
            Seriously, I am utterly confused… I’ve googled this issue over and over and it seems like I’m the only one with this problem. I cannot get this tool running in 10.6.x AT ALL. I’ve used 32-bit mode, doesn’t work. I dont see how people get this to work UNLESS they have a 10.5.x partition which they boot to run this program. If someone is running this in Snow Leopard, please give me some help on how they got it working.

  • Am 15. Dezember 2009 um 18:44 von Tim

    ZDNET Clock version 2
    Could someone make a 64-bit version of this? It won’t run when my Mac Pro is in 64-bit mode, running Snow Leopard.

    • Am 21. Dezember 2009 um 13:36 von chobar

      AW: ZDNET Clock version 2
      +1 for that

      Seems a shame that it doesn’t work on 64-bit Snow Leopard :-(

  • Am 8. Januar 2010 um 22:41 von stevew

    64-bit bitte
    Ein weiterer Antrag für ein 64-Bit dieses Tool zu kompilieren, bitte. (If only for Folding@home)

    • Am 26. Februar 2010 um 2:49 von Al

      AW: 64-bit bitte
      Could you please advice if it possible to over-clock Mac Pro 4.1


  • Am 27. Februar 2010 um 5:08 von Brien MacDougal

    Please make a overclocking tool for MacBook Pro 13 Inch 2GB ram 2.26 GHz.

  • Am 29. Dezember 2010 um 22:47 von RedEyes717

    kext module is missing – error under Snow Leopard
    Hi Guys,
    I did try all of the methods above, with no success at all.
    I’m under Snow Leopard and I’m keep getting the error ‚kext module is not found ..‘ (from the console messages).
    is there any workaround for this?

    thank you all.


  • Am 7. August 2011 um 21:22 von MM

    Lion + 64 bits
    Any chance of seeing this us full tool ported to compatibility with Mac Os X.7 (Lion)?

    • Am 9. August 2011 um 8:50 von Quicksilver

      Please 64-bit Version for Lion
      This would be VERY apprechiated. I use this tool for years and I love it. BTW: Overclocking in Snow Leopard and restarting in Lion doesn’t work for me.

  • Am 25. September 2011 um 18:09 von Enrico Sbardolini

    A prayer
    I would just like to use RAM at 800MHz instead of 677MHz on both iMac and MacBook Pro Core 2 Duo, 2.4GHz, with 800MHz FSB (2007).

    I think it would be a small thing to do for a utility of this power.

    Thanks, hoping at least one answer.

  • Am 18. September 2012 um 22:13 von Erwin Mul

    64-bit, running a macpro 1.1 on mountain lion (through chameleon) would like to try this.
    I had a freak unintentional overclock to 3.6Ghz from 2.0 after the first run of ML… Geekbench through the roof. Never reproduced it…

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