This Borg vessel had a complement of 64,000 drones, three of which occupied the dreamstate realm of Unimatrix Zero because of a recessive gene in their DNA makeup.

Those three were separated from the Hive mind in early 2377, thanks to a virus introduced into the Collective by the U.S.S. Voyager.

Cube 630 was patrolling Spatial Grid 94, when the Borg Queen noticed that their "voices" had become silent, so she caused the vessel to self-destruct in order to make a point to Captain Janeway.