Ik kwam bij MacOS Rumors deze posting tegen over het overklokken van de G4. Met enige moeite schijnt het mogelijk te zijn. De multiplier moet verandert worden en dat gaat niet mbv jumpers... en een BIOS ben ik nog nooit tegengekomen op een Mac :
First, the source noted that at Apple, one "fix" suggested to allow the company to ship 500MHz G4s was strictly clocking them to 499MHz. Few Mac users are aware of how imprecise processor clocking can often be -- machines sold as "400MHz" often actually run at 401.3MHz, for example. Because Motorola's first-release PowerPC 7400 chips contained a flaw that could cause them to be unstable at 500MHz or above, an attempt was made to allow all "500MHz" PowerMac G4s to run at 499MHz, avoiding the bug. The effort did not bear fruit because of the aforementioned inaccuracy of clocking; some machines still reached 500-508MHz, others went as low as 496MHz.
Although Apple itself can't work around the problem this way, some users of 400-450MHz G4s who wish to overclock may be able to. As with all overclocking operations, there is the possibility of causing damage to your machine, but....users with actual bus speeds of 99MHz or less (use a utility such as Powerlogix's G3 Cache Profiler to determine this) may be able to clock their processors to just short of 500MHz successfully and without encountering the first-release G4 bug. On the Sawtooth motherboard this involves soldering or the use of a third-party CPU with a bus-ration adjustment dial, but once the issue of CPU clocking is dealt with, even if the processor does in fact reach or exceed 500MHz, the instabilities introduced should be fairly subtle and can be avoided simply by clocking the machine back down.
The bottom line: all issues of pricing aside, the PowerMac G4 may be somewhat less limited for purposes of overclocking than once thought.
And, of course, the second overclocking insight we received from Apple: Sawtooth motherboards do, as with all other machines, include a set of resistors whose configuration controls the speed of its main bus. Our Apple source has successfully used PC133 SDRAM (hard to find, but it is out there) and a change of resistor configuration to send a Sawtooth to 133MHz main bus speeds. He was able to drive a test-seed 550MHz-rated G3 processor to 666MHz in the modified machine!