User configurable part number for the subsystem. When this column is empty: + The subsystem is not explicitly configured yet and any compatible, supported subsystem is allowed to boot. + If an existing subsystem is physically replaced with a subsystem of a different part number, the interfaces associated with the existing subsystem will be removed prior to adding interfaces of the newly inserted subsystem. When this column is configured with a part number: + The subsystem is explicitly configured to only allow a subsystem with that specific part number to boot. + Physically replacing the existing subsystem with a subsystem of a different part number will require adjusting this column to match the new subsystem. Otherwise subsystem won't boot. + To configure the device for a new subsystem, the user can change this column with a different part number. The interfaces associated with the existing subsystem will be removed and the interfaces of the specified subsystem part number will be created.