What are the capabilities/lmitations of 2 diffrent GPUs within the same PC (without SLI/Crossfire)?

[RedRioteer]

I am still fairly new to the computer technology scene, so sorry if I seem clueless in some way.

My PC has two graphics cards in it and each graphics card is connected to its own monitor. I have a GTX 960 (2gb) connected via HDMI to my main monitor (1920x1080) and a GTX 650 (1gb) connected via VGA to my sub-monitor (1280x1024). The main monitor is for gaming and the sub-monitor is to display additional information or content.

As I once understood it (without SLI or Crossfire) each GPU would function independently of one another. When playing a game, the frame rate on one screen would never match the other. However, I now know this is all wrong.

Recently, I was playing Fallout 4 on my main monitor while downloading content on my Xbox. I only had my main monitor to plug any HDMI cable into. So, to check on the download progress on my Xbox, I had to swap out HDMI cables. As expected, my PC shoved every program and desktop shortcut into the sub-monitor. I was certain I could not play Fallout 4 on the sub-monitor, however, I was curious to see how bad it would play. To my surprise, Fallout 4 didn't just play, it ran just as smoothly as it did on the main monitor. Aside from the HUD failing to scale correctly to the new resolution, the game ran perfectly fine.

But how did that happen. There was no way a GTX 650 (1gb) could run Fallout 4 that smoothly. Is there someway the GTX 960 (2gb) was helping the 650? was the 960 doing all the work and just displaying through the 650? Am I severely underestimating the capabilities of the 650? If these graphic cards can work together, how much are they able to do? How is this different form SLI/Crossfire?

 

[hang-the-9]

A 650 at 1024 resolution it will probably run Fallout 4 at near 30 FPS pretty steadily depending on the settings. Which is decently smooth.

Simple way to test, use one card at a time and run some benchmarks.