More than twice considering the fact that the second 64 doesn't have to house the OS.
Ah. When I see someone say "practically" I always associate it to being pretty much double the space, and meaning that it is under, but basically the same. (such as if the storage were to be 120, which would practically be double the space since a 64 is basically only 60, so 120 is practically double the space if you think of it that way)
ANYWAY
Technically it is exactly double the space.