Fun fact: The PowerMac G5 CPU cooling fan controllers have a failsafe mode: If the OS doesn't communicate with the fan controller, the fan controller assumes the worst: that the CPU is switched into the most power-hungry mode possible. To prevent potential damage to the CPU, after about 30 seconds, the cooling fans are cranked up to extraordinarily loud levels.

Apple didn't document how to control the fans. It took Microsoft a while to reverse-engineer the fan controllers. During that time period, using the G5s as Xbox dev kits required putting up with extraordinarily loud fans.

I can't find the photo with a quick google, but way back in the day an employee posted a photo of a TON of G5s arriving at Microsoft HQ.. supposedly they got fired for it, and it wasn't until a year or two later when the 360 was announced that everyone put two and two together.