Updated: May 17
All modern computers have lots of sensors. One of those are the core temperature sensor.
This is normally a Thermocouple that gets read by the motherboard and then this information can be accessed via BIOS or by a third party software.
What is a Thermocouple?
A Thermocouple is a sensor used to measure temperature. Thermocouples consist of two wire legs made from different metals. The wires legs are welded together at one end, creating a junction. This junction is where the temperature is measured. When the junction experiences a change in temperature, a voltage is created.
It’s worth noticing that these sensors are not always very precise. AMD is known for showing core temperatures way higher than the actual value.
The hard drive has a temperature sensor (or multiple temperature sensors – they might be used for internal control, self-test etc…) inside, and this data is passed through SMART.