Hi
The 6k is 1u switch no supervisor slots , the 4k in nexus is a blade itself , do you mean catalyst 6000 and 4000 as they are chassis based or the nexus 7000 is chassis based as well with SUP slots and it also depends exactly on the platform a 6513 and 6509 would have different SUP slots and 7009 and 7018 would be different etc , so you must check what platform you have then confirm where to put them as per the data sheet
The MSFC card best to read this explains exactly what each card does
https://supportforums.cisco.com/document/85621/understanding-msfc-pfc-and-dfc-roles-catalyst-6500-series-switch
