1# Multiple Chassis 2 3## Overview 4 5A BMC-based system can contain one or more chassis. A chassis is typically a 6physical enclosure that contains system components such as CPUs, fans, power 7supplies, and PCIe cards. 8 9A chassis can be stand-alone, such as a tower or desktop. A chassis can also be 10designed to be mounted in an equipment rack. 11 12For the `phosphor-regulators` application, the term "single chassis system" 13means the system type has a maximum configuration of one chassis. If the system 14type has a maximum configuration of multiple chassis, then it is considered a 15"multiple chassis system" even if the current system only contains one chassis. 16 17`phosphor-regulators` only supports powering on and off the entire system. It 18does not support powering on/off individual chassis independent of the rest of 19the system. 20 21## Defining the chassis in a system 22 23The [JSON configuration file](config_file/README.md) contains an array of one or 24more [chassis](config_file/chassis.md) objects. Each chassis object corresponds 25to a physical chassis in the system. 26 27## Differences between single and multiple chassis systems 28 29### System and chassis power state 30 31In a single chassis system, the system and chassis power state are identical. 32Both are either on or off. 33 34In a multiple chassis system, each chassis has its own power state. Even if the 35system is on, an individual chassis may be off. This can occur if that chassis 36does not have input power or has a critical hardware problem. 37 38See [Chassis Status](../phosphor-power-sequencer/docs/chassis_status.md) for 39more information. 40 41### Configuration 42 43In a single chassis system, regulator configuration is always performed on the 44chassis. 45 46In a multiple chassis system, regulator configuration will only be performed on 47chassis with the proper status. For example, a chassis that is missing or has no 48input power cannot be configured. 49 50See [Regulator Configuration](configuration.md) for more information. 51 52### Monitoring 53 54In a single chassis system, regulator monitoring is always performed on the 55chassis. 56 57In a multiple chassis system, regulator monitoring will only be performed on 58chassis with the proper status. For example, a chassis that is missing or has no 59input power cannot be monitored. 60 61See [Regulator Monitoring](monitoring.md) for more information. 62