Adding an external graphics card to an iMac

I was wandering if I can connect an external graphics card to my iMac....

Nope!

The OS won't address it and there is nowhere to connect it to. If you want a Mac that you can change graphics cards take a look at the Mac Pro's.

Hello,
Never heard of external graphic cards for the imac, and i cannot see where it should be connected to if they existed - You only have USB, IEEE1394, Ethernet, and compact flash inputs accessible from the outside of the Imac.

You can try it but I'm pretty certain it is not intended to work on an iMac. It also says it is intended to connect external monitors to computers. Why would you need this on an iMac when the iMac already has that functionality with a mini display port?

But let's get to the real question, why do you think you need an external graphics card?

Why do you feel you need this?

Well that depends on the iMac you get. If you get an iMac that has a graphics card that can handle gaming then you should be fine. Get one with the

ATI Radeon HD 4850 graphics processor with 512MB of GDDR3 memory

and you should be fine.

USB video devices like the one you reference generally offer fairly low performance. So while it would probably work, I think you'd find that it would not improve your game play but rather would offer significantly lower performance, if it worked with the game at all (many if not all of those USB video devices do not support OpenGL 3D acceleration) than the graphics processor built into any iMac.

The answer is "no", and it should be unnecessary. With the possible exception of Crysis, just about anything should run exceptionally well on your iMac (particularly if you choose one of the beefier graphics card options). The only better you can do is Mac Pro, which has slots for graphics cards and for which there are more options.

There are no "external" graphics cards per say. There are USB2 video adapters, however, the performance is exceptionally poor from the standpoint of games. USB2 simply doesn't have sufficient bandwidth to support video at the high frame-rates that you'd expect for an FPS. They are fine if you need a 3rd monitor for development work / editing documents, but otherwise useless for games. (Yes, most of the USB video adapters do have Mac drivers available).