Is there a way to tell how hot my CPU is running?

Software programs

The computer must have thermal sensors or an Intel Core Duo processor or later withDTS for you to be able to determine how hot your computer is running. Without the proper sensors, programs designed to monitor the temperature of your processor, video card, hard drive, etc. will not work.

• HWMonitor - A fantastic free program that displays the temperature of your CPU, each of its cores, your video card, hard drives, and the min and max values of each device. Below is an image and an example of CPUID HWMonitor.

• Core Temp - Another fantastic CPU and CPU core temperature monitor that is small and when minimized displays the temperature of each of the CPU or cores detected in the Systray.
• SpeedFan - Another good program capable of monitoring the temperature of your CPU, system, and HDD as well as displaying the fan RPM readings of each of the fans in your computer.
• Temperature Monitor (Apple) - Great free utility for Apple computer users to test their temperature on newer Apple computers.

Caution: It's possible for your computer to restart if it's not compatible with one or more of the above programs. Before running any of the above programs or similar programs make sure to save any open files in case your computer does restart.

Hardware

Heat probe

On the hardware side, you can install a temperature probe which attaches to the CPU. The other end of the probe attaches to a digital display console, which usually fits into a 3.5" or 5.25" drive bay. This console displays the temperature of the CPU. These probes can also be used on video cards, and some higher end probes feature multiple probes for monitoring more than one device at a time. For example, with enough probes you could monitor the video card, processor, memory, and hard drive. In the picture shown to the right is an example of the Aero Cool Touch-2100 that is capable of monitoring up to five different devices and adjusting the speeds of five different fans.

Temperature gun

Finally, there are also infrared temperature guns that are capable of determining the temperature of anything in the computer. A temperature gun can be pointed at the CPUheat sink to determine its temperature. Keep in mind that using this gun is only going to give you an estimated value since it cannot be directly pointed at the CPU with the heat sink attached.