Apple iMac 21.5", Mid 2011, 2.7GHz Intel Core i5, 4GB, High Sierra 1TB SATA HD | eBay
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Identify your iMac model - Apple Support
apple-history.com / iMac (Late 2011)
Apple iMac 21.5-inch 2.8GHz Quad-core i7 (Mid 2011) MC812LL/A-BTO | mac of all trades
Identify your iMac model - Apple Support
Apple iMac 27-inch Mid 2011 Technician Guide Service Manual | eBay
Amazon.com: OWC SSD Upgrade Kit for 2011 21.5-inch iMacs, Mercury Electra 1.0TB 6G SSD, 18" SATA III 6Gbps Data Cable, Installation Tools and iMac Screen Adhesive Tape Set : Electronics