Dell Dimension 4550 - Manual (Page 23)

Setting Up and Using Your Computer 23
HINT: If you are
connecting two flat-panel
monitors, at least one of
them must have a VGA
connector.
If one monitor has a VGA connector and the other one has a DVI
connector:
a Connect the VGA connector on the monitor to the VGA (blue)
connector on the computer.
b Connect the DVI connector on the other monitor to the DVI
(white) connector on the computer.
optional VGA
adapter