.

Considering this, do I need a SLI bridge?

You will need one of two SLI bridges: either the standard bridge (for less powerful cards), or a high-bandwidth bridge (for the more powerful cards). If you have more powerful cards (like say the GTX 1080), you can use a standard bridge, but it won't allow for the full performance of the cards.

Furthermore, what is SLI bridge? SLI Bridge Is a Simple Circuit Motherboard. Which Is Included With SLI-Capable Systems. The Scalable Link Interface (SLI) bridge is a simple, small circuit board which comes packaged with SLI-ready motherboards. The bridge has a connector on each end that attaches to the top edge connectors of SLI-ready video cards.

Consequently, can you use 2 GPUs without SLI?

Actually, you can, but it's useful only for a specific reason — if you have more than one monitor. So, if you have two monitors, and a system capable of running two graphics cards, and the specific use case scenario mentioned above, then you can use two cards without running them in SLI.

Can you bridge 2 different video cards?

Yes, this can technically work—both cards will give you graphical output. However, different cards cannot be linked together to function as a GPU array (CrossFire or SLI), so you generally won't be able to use them together to render graphics in games. The cards will operate independently of each other.