This article is from the Apple II Csa2 FAQ, by Jeff Hurlburt with numerous contributions by others.
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. -----------------------