Late 2009, 27 inch iMac can use 32 GB of 1333 MHz RAM, beyond what Apple says - YouTube
Apple iMac 27-Inch With 5K Retina Display (2017) Review | PCMag
A-Tech 32GB (4 x 8GB) PC3-8500 DDR3 1066/1067 MHz RAM for iMac Late 2009 27- inch (Quad-Core i5/i7) | 204-Pin SODIMM Max Memory Upgrade Kit at Amazon.com
A-Tech 32GB (4 x 8GB) PC3-8500 DDR3 1066/1067 MHz RAM for iMac Late 2009 27- inch (Quad-Core i5/i7) | 204-Pin SODIMM Max Memory Upgrade Kit at Amazon.com
How to Upgrade Memory in a Late 2009 21.5-inch or 27-inch iMac - YouTube
Apple iMac 2009 A1312 MB952LL/A 27" C2D E7600 3.06GHz, 12GB RAM, 1TB HD Catalina 885909286300 | eBay
Apple iMac (27-inch, unibody, 2009) review: Apple iMac (27-inch, unibody, 2009) - CNET
Memory Upgrades for Apple iMac 2009 - Up to 32GB
Max RAM for my iMac 27" (late 2009) | MacRumors Forums