updated 02:45 am EST, Wed November 14, 2012
Sporadic reports of lower thermal thresholds, GPU underclocking
According to scattered reports on the Apple Support Forums, some users who have applied Apple's latest extensible firmware interface (EFI) update are experiencing reduced frame rates while running graphically-intensive applications on the Nvidia GeForce GT 650M graphic chipset. The problems are inconsistent, and temporarily fixed by a SMC reset. The issue mostly affects waking a computer from sleep, gaming, or using Windows in Boot Camp.
Users report dramatic throttling of processor and graphical processing unit speeds when very conservative but high core temperatures are reached. One forum member claims to be seeing the speed reductions kick in at about 65°C, with a second drop at 80°C. The maximum temperature the processors are able to reach without damage according to Intel is 105°C.
Some speculation exists that the new lower thresholds and under-clocking of the GPU are intentional and were established to eliminate a persistent whine that is sporadically manifested when the computer is placed under heavy load, or to prevent overheating of the computer when in general use. Other theories suspect a miscommunication between the firmware and the thermal bridges used to monitor core temperatures.
MacNN is attempting to reproduce the issue and is performing some tests on specific thermal loads where the processor clock speed is reduced. This article will be updated with more information as it becomes available.