It depends.
Have them look at the schools they are interested in. I think
eventually all will go digital, but the requirements are different at
every school.
Some say digital. Some slides. Some you need you actually still need
to send the slide carrier. Other times you have an interview where you
are requested to show the work in person.
With digital sometimes all they require is putting a bunch of scanned
images into a folder. Others want a presentation that auto starts when
you insert the CD. (that can get complicated, if you don't have the
software).
Also some require more works in the specialty they are interested in,
others want a little of everything.