iMac (2007-2009) Memory Installation Video - YouTube
8GB Kit (4GBX2) DDR3-1067Mhz for Early/Late 2009 iMac and 2009-2010 MacBook Pro at Amazon.com
How to Upgrade iMac RAM (21.5" and 27" Aluminum): EveryMac.com
iMac 24-inch Early 2009 – Full Tech Specs, Release Date, and Price
OWC 6GB (2GB + 4GB) PC8500 DDR3 1066MHz SO-DIMMs Memory Compatible with Late 2008, Early 2009, Early 2010 MacBook, MacBook Pro Unibody Models, 2009/2010 Mac Mini, 2009 iMac Models at Amazon.com
OWC SSD Upgrade Kits For iMac Early 2009
A-Tech for Apple 2GB DDR3 1067MHz / 1066MHz PC3-8500 SODIMM Memory RAM Module for MacBook, MacBook Pro, iMac, Mac Mini - (Late 2008, Early 2009, Mid 2009, Late 2009, Mid 2010) Models at Amazon.com
Early 2009 duo core (square mac) now running High Sierra patch from Dosdude1 flawlessly. : r/mac
how to upgrade iMac early 2009 SSD and RAM - full class - YouTube