Exclusive: ZDNet overclocking tool enhances performance of Mac Pro

ZDNet Clock is easy to install. After downloading, you simply click on the ZDNet-Clock icon to start. Then the chipset and the clock chip are detected. The superuser password has to be entered at this point. The only computers currently supported are those equipped with Intel 5000 or Intel 5400 chipsets. That means all Mac-Pro and Xserve models with Intel processors. If the computer is not recognised the program closes with an error message.

The console can be used for diagnosing problems. It is to be found under "Applications – Utilities – Console". The ZDNet-Clock messages can be found in the "All Messages" window, see figure 3. When the chipset and clock chip have been detected the application appears as shown in figure 1 and figure 2.

The main control is the slider control, with which the frequency is set. The left-hand stop is always the standard frequency of the clock chip. "Underclocking" cannot be achieved with the GUI. Three frequencies are displayed above the slider control. "Bus Clock" displays the frequency that is actually generated by the clock chip. The front-side bus is also clocked with this frequency. As current FSBs are four times as wide as the original Intel FSB, Intel always indicates the quadruple frequency. ZDNet Clock calls this frequency the "Marketing Clock".

If you move the slider control completely to the left, 1333 MHz or 1600 MHz should be displayed there, depending on the model. The "CPU Clock" value should show the standard frequency of the CPU. To raise the frequency you slide the control to the right. You should not overdo it when overclocking for the first time. A good first move is to increase the "CPU Clock" by 10 MHz.

If you push the slider all the way to the right, to the maximum frequency, and click on the "Apply" button, the computer will certainly crash. The optimum CPU frequency with which stable operation is possible has to be worked out individually for each computer.

Increasing the front-side bus frequency raises the clock speed of the CPU without having to change the multiplier. The frequency of the Northbridge (MCH) is raised at the same time. So the memory is always overclocked as well. In the case of the Mac Pro, the CPU will normally tolerate higher overclocking than the MCH. As the Mac Pro uses fully buffered DDR2 memory modules (FB-DIMMs), which have error checking and correction (ECC), it is easily possible to feel your way up to the maximum stable overclocking frequency.

The console is used for that purpose. The "All Messages" window contains not only the messages from ZDNet Clock but also entries relating to corrected memory errors. Immediately after changing the frequency, entries relating to corrected errors will mainly appear, that are designated as a "correctable fbd error" or as "recoverable parity errors". They are caused by the switching of the frequency. The CPU and MCH briefly encounter synchronisation problems. This is normal, and there is no need to worry about it.

If further memory errors appear in the console after successful overclocking, this is an indication that you have exceeded a stable threshold with the overclocking. It makes sense to carry out a test after switching clock speed. Longer running benchmarks can be considered in this context, such as the prime number search program mprime. If no errors occur for several hours, you can assume secure operation.

In order to keep the effect of memory errors resulting from frequency switching to a minimum, ZDNet Clock overclocks the computer in steps of 1MHz (FSB). Tests have shown that an increase in the FSB by a large amount and the associated increase in the CPU frequency, for example raising the CPU clock speed from 2800 MHz to 3200 MHz, often puts the RAM modules so seriously out of synchronisation that more bits ‚topple‘ than error correction can pick up. This leads to a controlled crash. The memory modules report the error via NMI, the kernel acknowledges it with panic, see figure 4.

The result of step-by-step switching is that it takes some time for confirmation to appear after clicking on the Apply button. If you prefer direct switching, this can be selected by ticking the "Use Rapid Overclocking" checkbox.

Whether the switching can be successfully carried out depends very much on the RAM modules used. The first-generation tester (Mac Pro 1.1) is equipped by Apple with modules from Positivo Informática. In this case overclocking only works in very slow steps. The 2008 model (Mac Pro 3.1) comes with preinstalled Hynix modules. In this case, switching also works with "Rapid Overclocking" turned on.

ZDNet has also tested modules that do not come from Apple. Tests with modules from CSX equipped with memory chips from Elpida are disappointing. They run the Mac Pro clocked at 2800 MHz at a maximum of 2835 MHz. On the other hand, marginally more expensive proprietary modules from Kingston and Transcend (TS2GAPMACP8U-T) display no problems.

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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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