Apple 661-5945 Card, Video, AMD Radeon HD 6770M, 512MB - 21.5 inch iMac Mid 2011 - A1311. 661-5945 for A1311 21.5inch i5 2.5GHz Mid 11, A1311 21.5inch i5 2.7GHz Mid 11, A1311 21.5inch i7 2.8GHz Mid 11. Apple Video Cards for iMac (21.5-inch Mid 2011). Use this card as a replacement for 661-5944 (256MB) video card.