Q: I have a iMac (21.5-inch, Mid 2011) 2.7 GHz Intel Core i5 mac running on EL Captain and I want to purchase an second display. If i purchase an older iMac what ports does it need on the back for my current monitor to be able to use it as a dual screen

Q: I have a iMac (21.5-inch, Mid 2011) 2.7 GHz Intel Core i5 mac running on EL Captain and I want to purchase an second display. If i ... I have a iMac (21.5-inch, Mid 2011) 2.7 GHz Intel Core i5 mac running on EL Captain and I want to purchase an second display. If i purchase an older iMac what ports does it need on the back for my current monitor to be able to use it as a dual screen more