DRAC versus ERA/O ??

[H]

I just acquired two Dell PE 1650s.

I'm very familiar with the DRAC II on 2550s and DRAC III on my 2650s,
but what's the difference between DRAC and ERA/O on the 1650s?  It
looks like I can install either one, but I don't know what the
fundamental differences are.  Is one superior to the other, or do they
work together in some way?

thanks,
-Hank