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Saturday, June 28, 2008, 12:50 pm PT (03:50 pm ET)

Third-party tool allows Mac Pro overclocking

In a rare example of the PC's performance tuning culture translating to the Mac, a new utility has surfaced that lets Mac Pro owners overclock their systems beyond Apple's official specifications.

The German edition of ZDNet has posted a utility dubbed ZDNet Clock Tool that allows owners of the Intel-based Mac workstations to push the clock speeds of their Xeon processors significantly higher — with leaps from 2.8GHz to 3.24GHz for more recent systems.

Proven to work by those in the Mac community, the approach also increases the speed of the system bus and the memory as a result, though Apple's choice of hardware ironically suits it better to the process than many gaming-oriented parts for Windows computers: as the Mac Pro must use RAM with error correction, it prevents an excessive overclock from ruining data on the hard drive by making sure that only valid data leaves system memory.

The clock difference is enough to provide a tangible "free" upgrade in performance to the systems, though this isn't always measurable. In synthetic tests such as Geekbench, the software can incorrectly report similar performance even though timing the results proves that they're above what would happen at Apple's officially rated clock speeds.

However, unlike most overclocks, the technique requires a certain degree of trickery and carries an extra amount of risk. The current version of the tool works by loading a kernel extension into Mac OS X on boot that forces the clock speeds upwards immediately after the system starts. Without it, the Mac Pro would immediately revert back to its stock speeds the moment the system is rebooted, according to ZDNet. The initial beta app can also sometimes be overridden when the Mac comes out of sleep mode.

Like most overclocking, the technique is also limited by the nature of the hardware. At present, the German experimenters are unable to push past the 3.24GHz barrier without an inherently unreliable system. The faster processor speeds eventually overwhelm the memory and prevent it from correcting every error, triggering a kernel panic in Mac OS X that forces a reboot. High-performance third-party memory that operates above spec is described as the only real solution to this problem.

System time also falls out of sync without the expected clock rates and can't be corrected even by calibrating the computer online, the testers say. Instead, a reboot is necessary to at least temporarily provide accurate timekeeping.

While very much a beta version and potentially dangerous — the possibility exists that the system won't start up correctly — the utility is the first known that modifies core system performance on Intel-based Macs. Until recently, most overclocking utilities for Macs have dwelt on ramping up clock speeds on video cards to eke out more 3D performance for games.