Just The Facts : Which big cats only purr, and which only roar

I don't know about you, but I was under the impression that all felines, no matter what breed, could both purr and roar.  I know that Hermione (my kitty) definitely purrs up a storm (have you heard my latest show promo?), and I feel like she also tries to roar.  Sure it's not a big loud lion roar, but it's what I would assume a house cat sounds like when she tries to roar.  Either way, that's not so.  Some cats can roar and not purr, and vice versa.  Here's which is which..