In a computer, thermal sensors monitor the temperature of your hardware to prevent overheating. Computer hardware components, especially processing units like the CPU and GPU, get very hot and overheat if they are not cooled. Typical cooling methods for these components include heat sinks, fans, and liquid cooling systems. If the processor overheats, it malfunctions and quickly become physically damaged or destroyed. Many systems automatically stop running if their thermal sensors report an ambient temperature that exceeds a preset threshold.
Overheating is of special concern to users who overclock their systems. Overclocked systems necessarily generate more heat than their specifications, and require additional cooling to carry the heat away from the processors. In these systems, monitoring system temperature is a very high priority.
How can I check the temperature myself?
Some system BIOSes displays the values reported by the thermal sensors; third-party software packages are available for most operating systems which allow the user to monitor their system's thermal sensors directly. To find out what thermal monitoring is available on your system, check the documentation of your motherboard.