the 2 methods of linking the 2 units share information differently. if you can connect the 2 with an Ethernet cable, information is shared between the 2 units as long as both are on. if 1 goes off, any different info on that unit will not show up un the other.i have an older 798 linked with a newer 898 with an interlink. with an interlink, when you put in a waypint on 1, it is stored in the interlink and then sent to the other one. all the info is stored in the interlink, and both units have the same info whether the other is off or not. if both units do not have the Ethernet connection, you have to use the interlink. costs a little more, but works fine.