Can I upgrade the graphics card on my iMac?

I have not located anything on upgrading the video card on this machine. I would upgrade to the maximum RAM 8GB 1066MHz DDR3 SDRAM - 4x2GB. I couldn't see the specs on the hard drive on Apples site but a 7200 rpm hard drive would help and a solid state drive would do even better. I edited this to get in line with bac.

"Yes, it is possible to use Radeon HD 4850 graphics card but the problem that it is not possible to fit it inside because 4670 is physically smaller and there just isn’t enough room for it and the larger heat sink. But, you can upgrade to Radeon 5670 and even to 6750 graphics card from a 2011 21.5” iMac. With these the size of these cards & heatsink is the same.

The same situation with 27” iMac Core2Duo which have the Radeon 4670 graphics card, there you can use these Radeon cards: 4850, 5670, 6750 and 6770."

No its not possible. The GPU they are using in the Intel iMacs is actually the mobile variant. run a check on windows with the hardware identifier.

Yes you can use any Apple mxm 3 a/b graphics card it’s just plug and play…the letters a/b are the sizes, a/ being the smaller size for 21.5. The b cards although bigger can still fit by removing a piece of plastic, you’ll see what I mean once your in there… It’s really easy get yourself a step by step guide if you haven’t taken one apart before.