I just got my rMBP 15in 2015, this was a upgrade from my early 2011 17in. On my 17in in system prefs it has two sliders, one for display and one for system sleep. On this 15in it only has one for the display. I want the display to go to sleep but not the computer. This is making downloading large files impossible as my screen goes dark after 5 min, and unless i keep nudging the trackpad it stops downloading as the computer is now asleep. Does anyone know how to fix this?