Question on difference between Arcade, Pro, and Elite consoles

I was looking on Xbox.com and listed as differences between the systems it said Pro and Elite can play 300+ original Xbox games. I panicked because I just bought an Arcade console to replace my Elite that died on me. But when I went to play some of my favorite old Xbox games (Doom 3, Lord of the Rings), they played just fine on the Arcade console.

So, what are they talking about?

You need a hard drive to play original xbox games. Soo if you put your hard drive into the arcade version the games will still workxsplitsolo