TemperatureBefore moving on to overclocking we wanted to take a look at the temperature levels on the Ivy Bridges. In effect, while energy consumption is down, the temperature readings for the cores on the various monitoring tools are significantly up. To recap, Intel processors come with a Digital Thermal Sensor (DTS) for each core which reports to a register the temperature difference with the maximum temperature supported, expressed as TJmax. These sensors are less reliable as temperatures stray from the TJmax and even if they have been improved over successive generations, they’re still at a maximum error margin of +/- 5°C with an objective of +/- 2°C, which explains in part the sometimes significant differences in readings between the various cores. We’d like to thank Martin at HWiNFO for his help on this subject.
On Ivy Bridge Desktop the maximum temperature (Tjmax) has been increased to 105 °C by Intel, against 98°C on Sandy Bridge Desktop. Up until now, such maximum termperatures were above all found on mobile or server chips. Once this temperature is reached, mechanisms intervene to reduce the clock in a process known as throttling, so as to protect the processor. In practice we measured these mechanisms as kicking in at around 95°C on Sandy Bridge and 102°C on Ivy Bridge after switching off the fans on overclocked processors. These temperatures are of course higher than many users allow themselves to go out of fear of damaging their CPUs in spite of Intel's official specs. Processors shut themselves down completely at 120-130°C to avoid permanent damage.
[ Before Throttling ] [ After Throttling ]
Here are the readings taken on different processors in load in Prime95 with a room temperature of 25°C in load in Prime95 with a Noctua NH-U12P SE2 (tests outside casing). We give the average of four readings which allows us to reduce the impact of any margin of error:
- Core i5-2500K: 48°C (delta T of 23°C, 50°C margin vs Tjmax)
- Core i7-2600K: 51°C (delta T of 26°C, 47°C margin vs Tjmax)
- Core i7-2700K: 53°C (delta T of 28°C, 45°C margin vs Tjmax)
- Core i5-3570K: 56°C (delta T of 31°C, 49°C margin vs Tjmax)
- Core i7-3770K: 59°C (delta T of 34°C, 46°C margin vs Tjmax)
In spite of the reduction in energy consumption, temperatures are significantly up, with an 8°C increase on the i5 and 6 to 8°C on the i7. The main culprit would seem to be obvious, the increase in the number of Watts to be dissipated per mm².
In load in Fritz, the readings we took for the cores alone in HW Monitor were 61.2 Watts on the i7-2600K and 49.8 Watts on the i7-3770K but because of the new 22nm engraving the 3770K Ivy Bridge only takes up around 45mm² as against around 70mm² for the Sandy Bridge, which represents a reduction in area of 36%. This is a bigger difference than from die to die, which is 26% (160mm² vs 216mm²) because of the increase in IGP size. All this gives us the following:
- Sandy Bridge: 0.87 Watts per mm²
- Ivy Bridge: 1.11 Watts per mm²
Of course the cooling is carried out on larger areas: the die is bigger than the cores alone and is in contact with the CPU IHS (metal shell), which itself is in contact with the processor radiator, but with losses in thermal conduction each time. There also seems to have been a regression here as Pt1t
, which has taken an Ivy Bridge apart, notes that the contact between the die and the IHS is made by thermal paste instead of a metallic joint in indium, which offers better thermal conduction. The negative impact of this change seems marginal in practice as testing without the IHS didn’t show any notable temperature gain.
Nevertheless, in taking the maximum temperature supported on the Ivy Bridge desktop models up to 105°C, Intel has compensated for the increase in temperature and in the end we’re left with an almost identical margin for Sandy Bridge and Ivy Bridge with the same cooler, which means the cooling requirements for Ivy Bridge haven’t had to be improved. Those who like to keep their CPUs cool will however have to shell out for a more effective cooler.