As far as I know, motherboards have measured the CPU temperature for years by having a sensor "near" the CPU. This is the temperature that you will see in your BIOS with various motherboards and processors.
Additionally, at least modern Intel processors support thermal throttling. This means that these processors are able to somehow limit their frequency if they get too hot. The processor knows if it is "too hot", because it has a thermal sensor inside the processor die. This thermal sensor tells the processor how far it is from "too hot". As a side effect, software can also read how far from "too hot" the processor is.
If you run an application like HWMonitor and if you have a modern processor that has this kind of internal thermal sensor, you will probably see more than a single measurement from the "CPU". For example, I have "CPUTIN" that measures 33C now and "core #0" that measures 43C at the same time. The 33C is from the motherboard sensor, also read by BIOS. The 43C is an estimate that HWMonitor guesses based by the information of how far the processor is from it's "too hot" value.
It is said that Intel will tell how much "too hot" is during some funny event that takes place near this time. Or then they will tell something else.
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