When you shift in a traditional manual transmission, the clutch is disengaged and a sleeve is shifted from one gear to another. The teeth of the sleeve must align with the teeth of the target gear. Because the gears are different ratios (and therefore traveling at different speeds), the sleeve has a synchronizer cone which is pressed up against the target gear to match its speed before the sleeve slides all the way over.
As I understand it, a dual-clutch transmission is basically two smaller manual transmissions: one for the odd gears and one for the even gears. There are two clutches and when one is engaged the other is disengaged. Therefore, only the even or only the odd gears are in motion at any given time (I think?). This gives the advantage that the transmission sleeve can be "loaded" onto the target gear before unloading it from the active gear, then the active clutch is switched and the target gear is now active.
(Apologies if my usage of terminology is incorrect. This is all new to me.)
Is it true that, in a dual-clutch transmission, the target gear is stationary when the sleeve is loaded? Does a DCT require synchronizer cones?