Exclusive: ZDNet overclocking tool enhances performance of Mac Pro

When the first IBM PC clones that were clocked faster than the original at 4.77 MHz appeared in the eighties, games freaks noticed that many of their games became faster. The Cessna 182 of the Sublogic flight simulator flew at the speed of a Eurofighter. So the bus clock speed is in principle not a good source for real time.

Microsoft has now learned this, but clearly Apple has not. If you carry out benchmarks such as Cinebench or Geekbench after overclocking, the benchmarks do not indicate any improvement in performance at first. But if you resort to a stopwatch, the higher performance resulting from overclocking can indeed be verified. You also notice that the system clock runs significantly faster after overclocking the computer.

Mac OS with time problems after overclocking

Unlike Windows, Linux and many Hackintosh versions, Mac OS uses the bus clock speed as the time source. It is compared with real time when booting up. Nor does time correction by means of the Mac OS NTP daemon succeed: It simply no longer works with a large discrepancy between the bus clock and real time.

Whereas programmers of the IBM PC XT had to be forgiven for using the bus clock speed because of inadequacies of its Intel 8253 timer module, it should be reasonable to expect more from Apple, who now only offer computers with modern HPET timers. After all, multimedia applications use the HPET module. So videos do not run faster after overclocking.

The only option for „normalising“ the time of the Mac Pro again is to restart without switching off the computer. ZDNet Clock is fundamentally „reboot-proof“. But there are a few snags. The latest series of the Mac Pro (Mac Pro 3.1) can indeed be overclocked in the ZDNet test up to 3241 MHz while remaining stable. But a reboot without crashing is only possible up to 3178 MHz. Carefree overclocking fun does not exist beyond this frequency.

The first-generation machine (Mac Pro 1.1) is a little more problematic. If you program the clock chip the computer cannot be rebooted any more – not even if you select the factory-set frequency. So the clock running too fast becomes a permanent annoyance.

The fact that the latest version of Mac Pro (Mac Pro 3.1) can be booted after overclocking also means that a higher frequency is possible under other operating systems. That is of particular interest because there has to date been no functioning overclocking tool for Windows. In contrast, the first-generation machine (Mac Pro 1.1) can be overclocked under Windows with SysTool.

Problem with standby mode

After waking up the Mac Pro from standby mode, the clock chip is reset by the operating system to the standard setting, with the result that the computer runs at the standard clock speed again, despite the overclocking frequency. Repeated overclocking with ZDNet Clock also only works again if the kernel extension associated with the utility is first loaded from memory. That can be achieved very easily via terminal, by inputting the following command:

kextunload -b de.zdnet.kext.overclock

This bug will be remedied with a later version of ZDNet Clock.