A Japanese 867MHz Power Mac G4 owner claims to have souped his machine up to 1.067GHz with a simple (ish) flip of a few resistors on the new machine's motherboard.
On the underside of the Mac's processor daughtercard is a set of four resistors marked R1, R3, R5 and R7, respectively. Connected to two of them are circuit-making jumpers. According to the fellow's site, unsoldering the jumpers and reapplying them to different resistors changes the clock speed on the processor by adjusting the board's clock multiplier.
Adjusting the jumpers provides for a range of clock speeds: 733MHz, 800MHz, 867MHz, 933MHz, 1.0GHz and 1.067GHz.
The guy reckons to have run his 867MHz at 1GHz and still maintain system stability.
That said, there's a degree of diminishing returns here. For a 15 per cent increase in clock speed, the fellow only got a benchmark improvement of a fraction over 12 per cent. The PowerPC 7450 has its limits and start pushing it up beyond the gigahertz barrier and its efficiency starts to fall.
No surprise there - it's in the nature of microprocessor architectures to have these restrictions. It's why the Pentium 4 isn't expected to really come into its own until it hits 2GHz, for example.
It's also in the nature of processors that one part can run at various speeds. Processor makers test each chip at all speeds and sell it at the highest speed at which it will run completely without malfunction. The Japanese G4 owner has clearly been lucky enough to get a processor that is happy running at 1GHz - most other users are likely to be less fortunate.
After all, if Apple could safely clock up the G4 to 1GHz, don't you think it would be doing so? For all its talk of the 'Megahertz Myth' Apple would love to offer a 1GHz machine as much as its customers would like to buy one.
When Apple gets enough stable 1GHz parts, it'll release a machine at that speed.
In the meantime, if you're a Quicksilver G4 owner, should you try for 1GHz? This site shows you how, but we'd urge you to leave well alone. Soldering tiny resistors isn't a task for the inexperienced, and many old hands would pass on it since it's so easy to fry your processor this way. Go too far and in an instant your $2000 Mac is fritzed and by tinkering with the internals you've voided the warranty. Only proceed if you really don't mind rendering your Mac useless.
The site says: "Please note that any modifications you make to your Macintosh are made at your own risk," and so do we. You have been warned. ®