What Is the SMBus Controller?

The SM Bus Controller, also known as the SMBus or System Management Bus, is a set of integrated circuits, or chipset, located within a personal computer. It provides a two-wire interface that allows system and power-related components to communicate with other parts of the computer. The SMBus monitors voltage and temperature and can send a limited number of error messages when problems occur. Computer owners usually don't need to worry about this low level hardware device unless it stops functioning.

The motherboard of a computer is a printed circuit board that coordinates system processes and supplies power to other system components. In computer terms, a bus is a set of parallel wire connections between devices. A bus carries information about computer addresses, data and control. The SMBus is located on the motherboard and performs lightweight communication with the rechargeable battery, or Smart Battery System (SBS), and with temperature and voltage sensors, along with other devices like lid switches and internal clocks. The SMBus device includes a Processor Information ROM (PIROM) that's used to store read-only data about the computer's features.

The SMBus was developed by Intel Corporation in the mid-1990s to provide an inexpensive communication device for motherboards. The bus was originally available on Intel's Xeon chips. Its design is based on I²C (for Inter-Integrated Circuit, pronounced I-squared-C), an older bus developed in the early 1980s by Philips Semiconductor. SMBus is based on I²C and is generally compatible with it, but there are some major differences in the electrical specifications, protocols and supporting software. SMBus devices are supported by the Linux and Windows operating systems. They are also used on Intel-based Mac systems, where they are referred to as the System Management Controller (SMC).

A computer protocol is a set of agreed-upon rules used for communication between electronic devices. Messages that are transmitted by an SMBus consist of a series of 1s and 0s that are sequenced according to the SMBus protocol. SMBus devices and some I²C devices that adhere to this protocol can connect to the bus. Specialized devices that connect to the SMBus, like smart batteries and smart battery chargers, are not required to implement all of the commands in the SMBus protocol, but only the ones needed for their own simple systems.

The operating system of a computer communicates with the SM Bus Controller through a piece of software known as a driver. For the Windows operating system, applying updates or upgrading to a newer version can cause the SM Bus Driver to be uninstalled. In this case, you will most likely receive a system error message saying the SM Bus Controller hardware cannot be installed.

To solve problems with SM Bus Controller hardware, check the status of the device in the Device Manager dialog. You can invoke the dialog from the Windows Control Panel or by typing "Device Manager" in the search field at the bottom of the Start menu. In the Device Manager dialog, expand "System Devices" and look for the SM Bus Controller. An exclamation point displayed on the SM Bus Controller entry indicates an error condition. Right-click on the entry and select "Update Driver." Instructions for installing the driver software should be displayed. If this does not solve the problem, visit the customer support website for your computer manufacturer.

The System Management Controller on a Mac controls the fan, keyboard backlights, the battery indicator light and the lid sensor. Problems with these features could mean that the SMC needs to be reset. First, try powering down the computer and then power it back up. If issues persist, visit the Apple Customer Support website for details on resetting the SMC on a Mac.