  Large-scale resistive Hall-magnetohydrodynamic (Hall-MHD) simulations of the
transition from Sweet-Parker (collisional) to Hall (collisionless) magnetic
reconnection are presented, the first to separate effects of secondary islands
from collisionless effects. Three main results are described. There exists a
regime in which secondary islands occur without collisionless effects when the
thickness of the dissipation regions exceed ion gyroscales. The reconnection
rate with secondary islands is faster than Sweet-Parker but significantly
slower than Hall reconnection. This implies that secondary islands are not the
cause of the fastest reconnection rates. Because Hall reconnection is much
faster, its onset causes the ejection of secondary islands from the vicinity of
the X-line. These results imply that most of the energy release occurs during
Hall reconnection. Coronal applications are discussed.
