A missing driver does not usually cause an immediate system crash, but it creates subtle, performance-degrading issues. Common symptoms on Windows 7 include:

Transmits data from thermal sensors to control fan speeds.

Developed by Intel in the mid-90s, the System Management Bus is a simple, two-wire interface used for low-speed, system-to-system communication. Think of it as the internal postal service of your PC. It doesn't handle high-speed graphics or massive data transfers; instead, it handles the tedious but vital housekeeping. It allows the CPU to talk to the power supply, to check the temperature sensors on the motherboard, and to communicate with the battery subsystem in laptops.

Unlike USB or PCI, the SMBus controller implementation varies significantly between chipsets:

What is this mysterious component? Why does Windows 7 hate it? And more importantly, how do you make that yellow exclamation mark disappear forever?