Here's a rather specific update for iMac users running Tiger (specifically, 20-inch and 24-inch aluminum iMacs with 2.0, 2.4, or 2.8 GHz processors). According to Apple, Update 1.2.1 "...improves the performance and reliability of graphics-intensive games and applications and fixes an issue that some customers encountered when installing Mac OS X Leopard after applying iMac Software Update 1.2."
Check software update if you meet the criteria. Let us know if you have any problems.
AppleiMac 27-inch with Retina 5K display (late 2014)