Aside from this, successfully running the SLI configuration often proved difficult. At the time (as the case with the Voodoo2), some motherboards would not function with three video cards installed (i.e. 2D card, Voodoo2 #1 and Voodoo2 #2). In other cases, there were issues with conflicts as system resources in normal ranges were already accounted for, partly because many features that are today integrated into motherboards (such as the network interface and sound playback facilities) were at that time provided by add-on cards, each requiring additional system resources. Some systems lacked enough open PCI slots to support the setup and additional add-on cards were sometimes sacrificed.