Thanks for your suggestions. I ran all tests of the Passmark utility without major hiccups (leaving aside that my eight-year-old machine is no longer at the cutting edge, being down at about the 25th percentile score overall). In particular, it was marked down in the 3-D graphics test because it was unable to run this at its full native resolution, with evident chunkiness and some hesitancy. It was difficult to override the program’s default, which had the test window running on the laptop screen, but easy to drag the Passmark Control Panel over to the external monitor. During testing, I avoided using the mouse.
But at the end of testing, I produced an instant freeze when I clicked the maximise button on this Control Panel screen, attempting to use the external monitor’s fullscreen mode. This was the classic freeze described earlier, but (as I expected) after recovery there appeared to be no record displayed by Passmark of the underlying fault. I am not sufficiently computer savvy to use SAFE mode after reboot, for troubleshooting.
This latest freeze may link with your question about which screen is driven by which processor. My understanding is limited, and I was only aware of options offered by Nvidia to set defaults for particular programs, and I found no option for the user to decide what would drive a particular hardware screen. This may explain what I recently noticed in the Nvidia Control Panel regarding multiple monitors. This shows the laptop screen under the heading “Intel HD graphics family” and the ViewSonic screen under the heading “GeForce GT 540M”. Perhaps this answers your question without me consulting Microsoft? Bearing in mind my description of the way these freezes occur (only needing a mouse click to cause a crash, without necessarily running graphics-intensive programs), it appears to confirm a fault or flaw in the GT 540M. I am unclear whether this is a flaw inherent in all GT 540M’s, or just a fault in mine.
So, where do I go from here? Do I have any recourse to Dell/Nvidia, now that the laptop is out of warranty? Do I need a new laptop in order to run dual screens? -Ed