RC-50 Question

[Jeff Shirkey <jcshirke@midway.uchicago.edu>]

I've just watched a couple of the video demos of the RC-50 on Boss's  
web site. In multi mode, Paul Hanson loads a drum loop as one phrase,  
and then he has a guitar loop on another phrase (both of these are  
called up within the same preset, I believe). My question is where  
are these loops coming from? Are they something he has pre-recorded  
on his computer, for example, and he has imported them as wav (??)  
files into the RC-50?

Let's say I want to have a bass part as one phrase, a drum loop as  
another phrase, and a rhythm guitar part as another phrase, and I  
simply want to play over all of the above. Can I compose the bass and  
drum parts using a  VI and then import them into the RC-50? Likewise,  
if I wasn't composing/recording the rhythm guitar part on the fly,  
from where (and how) would I import it?

I guess what I'm asking is where these canned backing tracks are  
coming from, and how are they imported/stored in the RC-50?

Thanks,

Jeff