Hello,

I am trying to investigate whether there is a real possibility to upgrade the MXM graphics board in my iMac7,1 24 inch with ATI HD2600 board inside.

There are rumors flaoting the web from "it's soldered" (not true) to "you need a bios for the graphics from apple"...
My iMac has a MXMII / MXMIII board inside. I opened the iMac myself, the graphics board seems to be a totally standardized MXM device from AMD.

Look at the image attached.


So if you put another nVidia MXM board inside instead and install a appropriate nvenabler to Snow Leopard, is there still a reason why this could not work?

Click to view attachment

Theorically nothing is preventing you from doing it. However using NVEnabler would give you a black screen until GUI is reached.
A cleaner way would be to flash the video ROM with BIOS+EFI module, however, it's not that easy as you must bind that 2 ROMS together. Beside the required skills, the ROM chip is probably not large enough, and anyway, you'd probably not find a working EFI module for it. It seems some stuff is hardcoded and those can't be attached to an other card than the one they're designed for (even if GPU and stuff is identical).