Amazon.com: Original Graphics Video Card GPU Upgrade Replacement for Apple iMac 21.5 Inch Late 2011 Core i3 3.1 All-in-One Desktop PC MC978LL/A, AMD ATI Mobility Radeon HD 6750M, MXM VGA Board Repair
Upgrading an iMac GPU for METAL Support! Late 2009 – Mid 2011 Models - YouTube
Upgrade 24” iMac video card - ATI Radeon 256MB to NVIDIA GeForce 512MB - Ask Different
For iMac A1311 A1312 2011 2010 512MB HD 6750 6750m HD6750 hd6750m Vga Video Graphics Card
How to Upgrade/Replace GPU Graphics Card on Mid-2011 21.5" iMac - YouTube