So I found out about DSR through the NVidia control panel.
[Hidden link. Register to see links.]

Essentially, it will upscale the game to 4K then back to your native resolution (1080p/etc).
The increased sample points make it look better when downscaled back to native resolution.
The "smooth" filter that blurs it can be adjusted. I keep it less than 33% (as most people like to use 33 only).
Default settings are too smooth/blurry (uses gausian filter by default; no way to change this).

It works best if you can change the resolution in the game menu.

Changing the desktop resolution to 4K then launching game will give unexpected results. Like unscaled DPI/cursor/etc.
And telling Windows to fix blurry text (their new DPI scaling in Windows 10/Creators Update/Insider Program/etc), and setting scaling to 200% requires you sign out then back in for effects to take place.

But that's not all.

I've tried on lots of games and some games are just not compatible at all.

Tron Evolution doesn't seem to work with DSR. In-game. Have not tried in desktop then launch game method.
Age of Mythology (steam's HD upgraded version) doesn't seem compatible either. Capping at 1920x1080 in the game menu.
Among other games.

I'm aware of ReShade, but it doesn't always work nice with DSR (and MSI AfterBurner/RSST for screenshots in 4K before it gets downscaled).

D3D11 games work, but at a heavy expense on system resources.
My graphics card is only a Zotac GT 640 right now until I get my GTX 750ti back (or upgrade to something higher).
FFX the HD remake is D3D11.4, and it's brutal on mystem with DSR 4K.
Even with the lowest graphic settings for FFX and NVidia control panel forcing "highest performance" for all settings.

However, I did manage to get some games to work...

All screens were taken with MSI AfterBurner + RSST for full 4K rendering before it gets downscaled down to 1080p (my native resolution).

(click thumbnails for full resolution)

Star Wars: Empire At War (gold edition on steam):
[Hidden link. Register to see links.] [Hidden link. Register to see links.] [Hidden link. Register to see links.] [Hidden link. Register to see links.] [Hidden link. Register to see links.]

ObsCure (2004)
[Hidden link. Register to see links.] [Hidden link. Register to see links.] [Hidden link. Register to see links.] [Hidden link. Register to see links.] [Hidden link. Register to see links.] [Hidden link. Register to see links.] [Hidden link. Register to see links.]


The best one yet has been MOUNTAIN:
(albeit super heavy on the system, but not a game you need real time for)
[Hidden link. Register to see links.] [Hidden link. Register to see links.] [Hidden link. Register to see links.] [Hidden link. Register to see links.] [Hidden link. Register to see links.]

Hardware/software:
Intel(R) Core(TM) i5-3470 CPU @ 3.20GHz
Zotac GeForce GT 640 on GK107 GPU
GeForce driver: 398.36
MSI AfterBurner v4.5.0.12819
RivaTuner Statistics Server v7.1.0

---------- Post added at 04:37 PM ---------- Previous post was at 04:33 PM ----------

BTW, Nvidia goes by movie resolution (SMPTE UHDTV Standard): 4K = 3840x2160 (16:9 aspect ratio / UHDTV1).
It doesn't use 4096 width (DCI 4K).