When ProDOS boots, it will assume that LOADs, SAVEs, etc. refer to the main directory of whatever volume is in the boot Slot and Drive. It does not automatically establish a default volume or folder by name. So long as no default volume name is set, references to disks by Slot and/or Drive (e.g. CAT,S6,D2) will set the default device (by Slot and Drive) much as happens with similar commands entered from the keyboard under DOS 3.3.