class II radio?

How do I know if I have a class 2 radio? I am looking at the Terk XM direct unit which will only work on the class 2. So the question remains how can I tell?
anyone?
Thanks

Well I found out what that is, I was also able to hook up Sirius Satellite radio to the Equinox via a plug on the cargo area. Sweet deal. Direct satellite radio with out the stealership price.
Car did not come with XM but wired for it.
Just fyi if anyone is interested in direct satellite from the factory radio