my 16x pioneer dvdrom is udma 4, but only some dvdroms are. i haven't seen any cdroms or cdrw's that were anything but udma 2. dvdrw's, on the other hand... i imagine some would be udma 2 and some 4, just like dvdroms since they're max throughput isn't going to be any higher (16x is the fastest right now, right?). udma 2 can handle burning dvd's at 4x or even 8x just fine.