Quoted from the post,
"ATI Radeon HD 4870 graphics are available in the latest Mac Pro, while the ATI Radeon HD 4850 graphics power the latest iMac."
AMD?s World Renowned ATI Radeon HD 4800 Series Found In iMac & Mac Pro Complements Snow Leopard - Hardware Bistro
Link from my local website
"ATI Radeon HD 4870 graphics are available in the latest Mac Pro, while the ATI Radeon HD 4850 graphics power the latest iMac."
AMD?s World Renowned ATI Radeon HD 4800 Series Found In iMac & Mac Pro Complements Snow Leopard - Hardware Bistro
Link from my local website