ZDNet Clock works in Lion (Overclocking Mac Pro)

Okay, I finally did it. Upgraded to Lion all my Macs.

Why now, with Mountain Lion coming in a few weeks? Don’t know, just felt that way. I usually switch to another OS when it’s stable, but work and other commitments prevented me to switch to Lion until now.

When I upgraded my “inherited” 2008 Mac Pro (once at the office, now acting as a render slave at home), I wanted to try the good old ZDNet Clock tool.

For those unfamiliar with ZDNet Clock, it’s a simple app that overclocks 3,1 Mac Pros… by increasing the system clock!

This is not the best way to overclock anything, but I always found ZDNet surprisingly stable and reliable. If you go on an overclock spree and move the frequency slider all the way to the right, the Mac Pro won’t boot anymore, but once you find the sweet spot for your system it can bring a 10-15% speed increase without hassles.

For my 2008 8 core Mac Pro, clocked at 2.8Ghz, the sweet spot is around 450Mhz, a 12% speedup. Not too shabby.

However, ZDNet clock does not work under Lion and there are a lot of posts around about this, with update requests, and some people advocating to keep a Leopard partition just to run it.

Fact is, it does work just fine with Lion. It does not work when the 64bit Mac Os kernel is loaded, but it does work under Lion if it’s run under the 32 bit Kernel.

The issue seems to arise because Lion is the first Mac OS to boot with 64bit kernel. Snow Leopard required to switch to the 64bit kernel for testing purposes.

So if you get the “unsupported” error, and yet you have a 2008 Mac Pro (it won’t work on 2009 and 2010 models), the most likely reason is that the 64 bit kernel is on.

Just reboot, keeping the keys 3 and 2 pressed during the startup (from the chime until the apple logo shows up).

Start the overclock app, set the frequency, then reboot again to fix the system time issue. And here it is, a faster Mac Pro under Lion.

Have ten percent more fun!


  1. I have success with a small boot partition in 10.5 set for zdnet overclock…
    I then reboot into lion 64 bit and it works fine!

  2. Thanks a lot for the tip ! It works like a charm. I was so missing it since my upgrade to Lion. The reboot in 64 bits works too. Here i come : stable 2800 to 3248 Mhz ! (+ 16%) with 8 x 1 GB of Kingston ECC RAM.

  3. Stick 2 X5482’s in & you will be good for 3.55Ghz, speeds up your graphics card to boot! Mountain lion is going to require a new strategy as no 3+2 32 bit startup option. I’m setting up 2 boot partitions on SSD one for lion & the other for mountain lion. The plan is to boot 32 bit lion, run ZDnet & then boot mountain lion. Or Boot windows, overclock with setfsb to 3.2, reboot into mac.

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