iMac G5 processor attenuation

Yeah it just throttles down the voltage.
I also have a rev. A iMac. I'v never fried the CPU or MB. But sometimes, on a hot day, under full load, it will automatically power down.

 

I don't know how the G5 handles it, but there are a couple of ways to do it. Some chips support this natively and either the FSB, or the multiplier is changed speed up and slow down the processor. This is very typical of mobile processors such as the Pentium M and Core CPUs from Intel.

Another approach (typically used in cheap PC laptops that use desktop processors), is to have the OS send sleep commands to the CPU at a certain interval (ever second operation for example). This causes the CPU to idle a certain amount (sometimes there's only 1 actual operation and 3 sleep operations...essentially reducing the processor speed to 1/4 of the original speed), causing less heat. This approach isn't always that good, but if the processor doesn't support speed scaling natively, you don't really have any other choice.

 

So what happens when it throttles down the voltage? (I know about the voltage, but performance wise. )

I notice a big slow down from automatic to reduced. I just dusted out my G5's CPU duct. It was packed with dust.

Err..nevermind.