как подключить две видеокарты crossfire

Asus Radeon HD 4870 X2 Top (EAH4870X2 TOP/HTDI/2G/A), HIS Radeon HD 4870 X2 (H487X2F2GP), MSI Radeon HD 4870 X2 OC Edition (R4870X2-T2D2G-OC), Sapphire Radeon HD 4870 X2 (HD4870 X2 G2 GDDR5) | Тест | THG.RU