My i5 / 580 iMac has arrived! So, w.r.t thermals:
– maximum load with Prime95 initially draws ~77W from the CPU. But this drops to 70W (thermal throttling!) and the fan goes to 2700 rpm. Stable at around 95 degrees and 70W power consumption.
– medium load with Prime95 (two cores) draws ~45W. Fan slowly fluctuates between 1200 and 1600 rpm. CPU temp 90 degrees.
The following are with Unigine running in the background:
– two loaded cores with Prime95 + Unigine Valley (50W CPU power usage total) = CPU core temp 95 degrees, GPU core temp 77 degrees, 2700 rpm fan. I cannot get the CPU to consume more than 60W. Notably, the FPS during Unigine do not drop, so it looks like the GPU keeps its cool nicely. It will not throttle.
– as soon as I quit Prime95, with Unigine still running, the fan goes to 1900 rpm and stay there. GPU die temp stays at around 77 to 80 degrees.
– if I start Prime95 again, but with only one thread (35W CPU draw), the fan spins down to 2300 rpm.
Ambient temperature is a toasty 25.5 degrees. Idle temps are about 46 degrees for CPU and GPU. All chip temperatures given are the
die temperature. Not something nearby the CPU or GPU, but the temperature of the chip itself.
I conclude that the Intel CPUs run pretty warm. Even the fastest i5 is thermally-constrained. Although you need to push the CPU with a heavy sustained load in order to ramp up the fans, it's these loads that the i7 is good at. However, the i7 will probably throttle down to the same speeds as the i5. I would really advise against getting the i7 just for the sake of getting the highest specs – only get it if you really need it. And even then, it probably won't be much faster due to thermal constraints.
Most games shouldn't cause the fans to spin up to max, unless they're very CPU intensive. Especially if you use vsync to cap the framerates, so GPU utilization is lower than 100%, you should keep the iMac running cool and quiet.
If I guesstimate that the GPU can sustain using 95 W of power, this shows that there is a considerable difference between the iMac's ability to cool the CPU vs the GPU. Perhaps the difference lies in the fact that AMD solder the heat spreader to the chip, whereas Intel use a thermal paste. It's a bit strange.
A few other thoughts:
- the minimum brightness setting is really dim. Even dimmer than my 2012 rMBP. I love it!
- I do not notice the fan at idle. If I put my ear to the case, I can hear the fan motor (and maybe even the ticking noise people are talking about), but IMO it's much ado about nothing. In a quiet room, sitting in front, I can only just hear the very faintest rushing of air at idle. When sitting in front of the iMac I never hear the noise of the fan motor itself, no matter what the fan speed – only the rushing of air.
- The fans at maximum speed are much less annoying – and subjectively quieter – than my rMBP.
- the screen is amazing!
