Most computers support “Health Monitoring” in their BIOS where you can view temperatures and fan speeds. This is useful, however not ideal since you have to reboot your machine to see it. If your system does not include monitoring software which can be installed on Windows, then take a look at SpeedFan.

From their website:

SpeedFan is a program that monitors voltages, fan speeds and temperatures in computers with hardware monitor chips. SpeedFan can even access S.M.A.R.T. info for those hard disks that support this feature and show hard disk temperatures too, if supported. [...] At the lowest level, SpeedFan is a hardware monitor software that can access digital temperature sensors, but its main feature is that it can change fan speeds (depending on the capabilities of your sensor chip and your hardware) according to the temperatures inside your pc, thus reducing noise.

My motherboard did not come with software to monitor hardware temperatures which can be loaded into Windows, so SpeedFan is a great utility. Personally, I don’t mess with any fan speeds, but if you want to tweak your system to make it run a little quieter or cooler, try out the advanced features.