Hi everyone.

I'm currently testing the difference between VGA and DVI when it comes to dos games (especially Jazz Jackrabbit), and I'm a bit surprised by the results. At first I was annoyed by the time needed by my LCD screen to refresh each time there is a change in the video mode (it goes blank for 3,5 seconds which is huge) so I wanted to check if it's related to VGA.

Setup:

I ran my tests on a LCD screen that has dual input (VGA / DVI) and I tested on 2 computers. The first one has a Ti4200 graphics card, the other one has an Intel Integrated 82865G.

Test:

Pretty simple, I run the first level of the first episode of Jazz Jackrabbit, and I navigate through the OSD of my LCD screen to display video informations.

Results:

Ti 4200 VGA :
- H 31.25 kHz
- V 59.29 Hz
- Pixels 27.90 MHz
- Res 720x400

Goes blank for 3,5 seconds when there's a change in display mode, which is often (for example between the planet loading screen, and the beginning of the level in Jazz Jackrabbit).

Ti 4200 DVI:
- H 64.17 kHz
- V 60.19 Hz
- Pixels 108.03 MHz
- Res 1280x1024

Always stays at 1280x1024 (through I doubt it's somehow upscaled), no blank screen, which is perfect. A proper way to enjoy the game without interruption.

Intel Integrated 82865G VGA:
- H 31.41 kHz
- V 59.60 Hz
- Pixels 27.90 MHz
- Res 720x400

Has the blank screen issue when the video mode changes.

Intel Integrated 82865G DVI:
- H 31.50 kHz
- V 59.77 Hz
- Pixels 27.80 MHz
- Res 640x398

And... it's still has the blank screen issue when switching video modes (Jazz menu is @70Hz).
Also note that all values seems really close between VGA and DVI, except for the resolution.

I'm confused

With the Ti4200 + DVI I'm getting fantastic results, while the Intel 82865G seems disappointing.

From this point I have three hypothesis:
- The Ti4200 has an builtin upscaler, which sends a 1280x1024@60 Hz stable signal to the screen through DVI. That would lead me to another question => why it does not work on VGA ?
- The 82865G lacks some DVI features, which leaves the screen unable to work in a constant mode.
- The 82865G works as intended, it does not tries to upscale anything, just send the signal "as it is" to the screen.

I'm basically trying to figure out if any of these card works "too well" or "too bad".

Thanks !