Display in Safe Mode vs. Normal Mode

Late 2006 iMac recently started to have constant freeze up issues and horizontal lines in display. From what I have read, the likely culprit might be a video card. But I noticed, when the iMac starts up in Safe Mode, the machine operates fine and with no random horizontal lines in display. My question, what system items related to display/video are not loaded in safe mode that is making this difference ?