OS 9 on unsupported 7447a CPU's maybe a little tricky.
It seems on portable models, the CPU multiplier boots in DFS mode, meaning reduced CPU speeds under OS 9, because we have no software to put the CPU in High Performance mode.
Specifically SPR 1009 ( HID1 ) bit 9.
Does anyone know of any OS 9 software that can read or write to SPR's?
Is there a way to set the SPR via Open Firmware?
If we had a way to set/unset this bit under OS 9, we could get the stealth upgrade 1.5 Ghz Mini to operate in DFS mode.
Desktop systems are not affected because the 7447a doesn't support 1/4 multipliers in DFS mode. Meaning if your desktop Mac has a CPU that is x.5 x the bus speed, it wouldn't support DFS, unless you changed the multiplier to be a whole number.
Also, the 1.5Ghz Mini would support DFS as the Multiplier is 9x 167, however it lacks PRIM_Info, so OS X won't show that option in the Energy Saver Control Panel.
Setting the correct bit in the PRIM_Info would make the option appear in OS X and OS 9, however OS 9 lacks any code for the 7447a, so it can't change the Performance Mode of the CPU.
Likely, if we knew more about the Apple CPU Plugin, we could patch it to support DFS on the 7447a.
If you have a 1.5Ghz Mini, running OS X, and you would like to test DFS, install CHUD Tools and use ReggieSE to set/unset bit 9 of HID1.