Twinfin 12 is the model, 6.0 is the version of the Netezza software running on your Twinfin 12. I don't think there is a way to know what model your system is directly (that is, there is no select statement that is going to say "this is a TwinFin 12". You can look at the _v_spu view to see how many SPUs (aka s-blades) are in the system, or the _v_dslice view to see how many dataslices are on the system.
For a detailed list of the physical components in the system, you can look at the _v_hw view.
