Each HD core system (HD1, HD2, or HD3 ) comes with one 12' DigiLink cable, for the purpose of connecting a 192 I/O or 96 I/O to the HD Core Card. Each 192 I/O or 96 I/O comes with a 1.5' DigiLink cable, intended for chaining a second 192 I/O or 96 I/O to its Expansion Port. Given this, if you have three, five, or seven HD I/Os, you most likely will want to purchase an additional one, two, or three 12' (or longer) DigiLink cables respectively, to connect to HD Process Cards.