Apple iMac (27-inch, September 2013) review: New processors and faster Wi-Fi for Apple's slim desktop - CNET
iMac (27-inch, Late 2012) - Technical Specifications
iMac 27" A1419 Late 2012 Logic Board W/Nvidia GTX 680MX GPU *No CPU* - Gamers Arena Custom Computers PC
For A1418 Motherboard 820-3302-A Logic Board Apple IMAC 21.5'' GT640M 512M GPU Late 2012 100% Test OK - AliExpress
iMac 27-inch Late 2012 3.4 Ghz Intel Core i7 24 GB Memory NVIDIA, Computers & Tech, Desktops on Carousell
Amazon.com: Original Graphics Card GPU Replacement, for Apple iMac Late 2009 A1312 MC507LL/A 27-Inch Core i7 2.8 27-Inch Computer, AMD Radeon HD4850 HD 4850 GDDR3 512MB, MXM GPU Video Board Repair Parts :
iMac Intel 27" Graphics Cards | iFixit
21-inch iMac teardown shows newly rearranged innards | Ars Technica
iMac (27-inch, Late 2012) - Technical Specifications
Review: 21.5-inch 2012 iMac takes two steps forward, one step back | Ars Technica