The System Management Bus (SMBus or SMB) is a simple, two-wire communication protocol that is primarily used for lightweight communication in computer motherboards and embedded systems. It is based on the I2C (Inter-Integrated Circuit) protocol, but it imposes stricter electrical and protocol specifications, making it a more defined subset of I2C.
SMBus was originally defined by Intel in 1995 for system and power management tasks, such as communicating with smart batteries to read their remaining capacity, querying temperature sensors on the motherboard, or controlling fan speeds. It operates as a master-slave bus, similar to I2C, using a clock (SCL) and data (SDA) line. Because it is designed for low-speed, on-board communication, it is not used for high-bandwidth data transfer.
The PMBus (Power Management Bus) protocol, which is specifically designed for controlling digital power supplies, is an extension built on top of the SMBus protocol, adding a standardized command set for power management functions. Therefore, SMBus provides the foundational communication layer for many modern digital power management and system monitoring applications.