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-power-sequencer` 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## Differences between single and multiple chassis systems 18 19### System and chassis power state 20 21In a single chassis system, the system and chassis power state are identical. 22Both are either on or off. 23 24In a multiple chassis system, each chassis has its own power state. Even if the 25system is on, an individual chassis may be off. This can occur if that chassis 26does not have input power or has a critical hardware problem. 27 28See [Chassis Status](chassis_status.md) for more information. 29 30### Chassis power good faults 31 32If a single chassis system experiences a power good (pgood) fault, the system is 33powered off. 34 35If a multiple chassis system experiences a power good (pgood) fault in one 36chassis, the system will be powered off and then powered on again without that 37chassis. 38 39See [Power Good Faults](pgood_faults.md) for more information. 40 41### Brownouts 42 43If a single chassis system that was powered on experiences a brownout, the 44system will be powered off. 45 46If a multiple chassis system that was powered on experiences a brownout in one 47chassis, the system will be powered off and then powered on again without that 48chassis. 49 50See [Power Loss](power_loss.md) for more information. 51 52### Blackouts 53 54If a single chassis system that was powered on experiences a blackout, the 55system loses all power. It will be completely off until utility power is 56restored. It may then automatically power on again depending on the Auto Power 57Restart settings. 58 59If a multiple chassis system that was powered on experiences a blackout in one 60chassis, that chassis loses all power. The system will be powered off and then 61powered on again without that chassis. 62 63See [Power Loss](power_loss.md) for more information. 64