I use a mid-2007 iMac with 4GB ram (that is max on my machine) and I ran dual using Parallels. I don’t recommend it but you certainly can run dual. FWIW, I backed out El Capitan due to issues with wifi. Seems my older chipset is never going to work right with the new OS’s so I am stuck at 10.10.5. I’m not even sure switching to a wired network would allow me to upgrade to the newer OS. 