We have three INS units, two of which are managed through a FMC, and crosslinked. Each INS has it's own dedicated GPS GNS input directly to the INS and the FMC has it's own GPS input as well.
The third INS, a Litton 92, has a dedicated GPS input which we also don't see. the Litton is only good for (I believe) 6 hours Class II without the GNS input, but it's good indefinitely with it. It doesn't work through a FMC or FMS; it's autonomous and has dedicated GPS input to the INS itself.