Here's How to Force Your Mac to Run Only in 64-bit Mode- The Mac Observer
IMAC - 123myIT
Apple iMac (spring 2011) review: Apple iMac (spring 2011) - CNET
Amazon.com: Original Graphics Video Card for Apple iMac 2011 Core i5 2.7 A1312 MC813LL/A MC813 27 Inch Desktop PC Computer AMD Radeon HD 6770M HD6770M GDDR5 512MB 109-C29557-00 Replacement Parts : Electronics
A-Tech 32GB (4x8GB) RAM for Apple iMac (Mid 2010 27 inch 4-Core, Mid 2011 21.5/27 inch) | DDR3 1333MHz PC3-10600 204-Pin SODIMM Memory Upgrade Kit at Amazon.com
Refurbished: Apple Desktop Computer iMac MC978LL/A Intel Core i3 2nd Gen 2100 (3.10 GHz) 4 GB 500 GB HDD AMD Radeon HD 6750M Mac OS X 10.12 Sierra - Newegg.com
apple-history.com / iMac (Late 2011)
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Apple iMac i5 21.5" AIO Desktop Computer Core i5 2.5GHz 8GB 500GB Sierra 2011 and WIFI