SM Bus controller is your Systems Management controller. This is a part of your chipset drivers, usually intel based chips. If you've just done a recent install, you probably just installed windows and not your motherboard/chipset drivers. They're not exactly ESSENTIAL, but to get best performance, you'll want them to be installed. It's a basic basic communications controller between things on your motherboard.
What motherboard do you have? If you still have the CD that came with the motherboard, go ahead and pop it in and install the drivers on it.
If you don't have the CD, but you know what motherboard and chipset you have, go to the manufacturer's website and download the proper drivers.
If you don't know what motherboard you have, and have no CD's, you can download a free program named "Everest Home Edition" that will tell you more than you ever wanted to know about your computer.
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