1.2. SYSTEM TYPES
Bus systems generally use one or more IPMBs (a sister standard to IPMI) to interconnect the various components for management. IPMB is a modified I2C interface; it provides for a somewhat slow but simple communication bus.
The boards can generally be individually power controlled, so even though a board is plugged into the system it may be turned off. The shelf managment controller may implement some policy, such as fan controls or auto-powering up boards, but is generally used as a conduit for an external management system to control the parts of the system.
Individal SBCs vary on whether the local Management Controller is connected to the microprocessor on an SBC. Some are, and some aren’t. This connection has some limited usefulness if the software on the SBC wishes to obtain local information from the IPMI system or store logs in the IPMI event log.
These types of systems are used to achieve high density in places with expensive real-estate, like a telco central office. As you might imagine, you can pack a lot of processing power into a small space with a system like this. Since they are generally designed for hot-swap, and can have I/O come out the back of the system on separate cards; it makes mainenance easier.