When you make a request to Register, Waitlist or Drop, at the bottom of the screen is a drop-down box:
If you choose PART - then the computer will process whatever actions it can. For example if you wish to drop one section and add another, the computer will drop the one section, even if you are not able to add the other section. Caution: Be careful to not inadvertently drop a section without adding a new one if the add section is full. Best to use PART only when adding sections.
If you choose ALL - the the computer will process all the actions if all are possible, or none of the actions if all are not possible. For example, if you wish to drop one section and add another, the computer will not drop you from the one section, if you are not able to add the other section. Both actions must be 'doable' for the computer to process them. This is a safer process when dropping a course.