It’s been a while since Apple originally acknowledged freezing with their new aluminum iMacs. But since then, many users are still having problems. AppleInsider has started to wonder if the problem is not a software error, but a hardware issue caused by overheating.
https://gizmodo.com/ati-graphics-may-be-at-the-root-of-imac-freezing-issues-307409
One specific symptom that some users have experienced is a series of graphical glitches before their computer freezes up. Such glitches are the same you’d see in an overclocked video card that’s running too hot. And apparently upgrading to Leopard often exacerbates the problem, at least according to one Apple thread—which makes sense, since Leopard takes advantage of video chipset processing throughout normal OS functions, adding fuel to the not quite literal fire. Anyone out there having problems? [appleforum via appleinsider]
