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Does the Bios Lie?



A friends told me that CPU temps in the bios can sometimes be hotter than the actual CPU temp by around 10'C

Is this true, and does it apply to most systems?

Im running AthlonXP 2700+ on a Soltek SL-KT400-C

According to MBM5, my Case Temp average is 35'C,
(LOW- 34'C HIGH- 43'C)

CPU Temp average is 44'C
(LOW- 39'C HIGH- 59'C)
at the time of writing this my cpu temp is 40'C


hardware monkey
i don't see why that would be. i'm sure manufacturers attempt to get as accurate a reading as possible. though i'm sure the difference from one board to the next could be off by quite a few degrees, i don't see why they would all be higher or lower across the board.

your temp readings are also affected by what type of thermal diode you have and how it's situated in the socket. some are right on the pcb so are far from the cpu surface.. therefore probably not giving you accurate temps (they would lower than actual, if anything). if you have the kind that stands up, you'd be best to bend it up, put a dab of thermal compound on the tip, and install the cpu so that the diode will be up against the bottom of the cpu and, along with the thermal compound, will give you as accurate a reading as you'll get without extra temperature sensors.

and if you're differentiating between bios and windows temperatures, they should be the same. if not, look into a bios update or updating/changing your temperature monitoring software.
Also, while some boards will read the thermal sensor on the mobo, some read the thermal diode in the CPU itself. Since the diode in in the CPU, it will be more accurate and most likely higher than one mounted on the mobo. Either way, BIOS revisions DO make a difference sometimes as the temps may be calculated differently between two versions (my board is a good example of this).
The temps can be hotter or COOLER by 5-10C degrees. Gigagbyte, or maybe it was Tyan, messed up a temperature correction algorithm on one of their bioses and was way off once. I also see many posts in here about people getting different readings from Sisoft, Sandra, the Bios, the MB manufacturers monitor program, etc. The accuracy of the temp reading is no better than the software "digitizing and correcting" the analog signal. I've seen the same CPU/HSF in the same case, with the same case and outside temperatures read from 45-55C when switching between 3 different MBs.

The next big contributor is whether the bios uses an external thermal sensor under the CPU or the thermal diode on the CPU. That varies by MB, CPU type, etc. The "under the CPU" sensors can get dirt and finger oil on them, be pushed down during CPU installation so they are not actually in contact with the CPU, etc.

The third factor is the accuracy of the (external or internal) thermal sensor. These parts vary a few percent from lot to lot when built. The accuracy of the thermal sensor will also change as the thermal sensors ages, gets heated and cooled and undergoes vibration (from the fan). Typical commercial parts rated at 2% initial accuracy will go to about 12% at "end of life".

Bottom line, be conservative. The thermal readings you see are not that accurate (even more so with AMD CPUs than Intel). Aim for a system temp of ~35 and a CPU temp of 45-50. Then if the sensor is reading low 5-10 degrees you are safe.

The one thing the sensors are reliable for is showing you a relative change (like if the system is getting dusty or a case fan died.)


thanks for you replies! having fiddled it alittle I seem to have reduced my temps alittle more just to safeguard myself. :)

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