It will be better to make new topics, if somebody want do this iMac CPU bus overclocking.
>There seems to be some confusion. U4 is CPC945, while CPC925 is U3/U3H.
>Changing the ratio on the fastest iMac (2.1 GHz) from ⅓ to ½ would result in 1.05 GHz (as you wrote >in
>comment #19), so testing 1.25 GHz isn't possible this way. What's the maximum frequency a "lite"
>version of the U4 would be able to run at in your opinion?
1.25 GHz is mentioned, because we know that 1.25 GHz of certain U4 / CPC945 version is possible ( Powermac Quad have 2.5 GHz with ratio 1:2 ). It means if in Quad is the same chip (with the exact same code) as on your photo, it will be safe from max. frequency point of view.
I don't know, what "lite" version means. I only know, that in older Powermacs is U3 and in older iMacs U3 lite. Similarly there can but cannot be U4 lite version for newer iMacs. Of course, it cannot means limited frequency, but for example bus for only one CPU, who knows.
If this photo is Northbrige from your real iMac, it is possible to find according manual. Codes on top of CPU contains also revision number. Probably revision number is also part of this northbridge code. You need the same manual version (or higher) as Northbridge have. And check frequencies and PLL configs.
And there is also second thing. In link in post #18 there is in the bottom some comments. There is said, that now he have overclocked bus frequency 900 MHz with ratio 2:1. Unfortunatelly it fits to two older different iMac models: iMac G5 1.8 20" or iMac G5 1.8 17" (ALS). So we are absolutely not sure, if resistor numbers in iMac iSight are the same, because this type is much different.
AmigaOS3: Amiga 1200
AmigaOS4: Micro A1-C, AmigaOne XE, Pegasos II, Sam440ep, Sam440ep-flex, AmigaOneX1000
MorphOS: Efika 5200b, Pegasos I, Pegasos II, Powerbook G4, Mac Mini, iMac G5, Powermac G5 Quad