Check my DOSBox Tutorial (YouTube video). Especially the section about scaler options and resolutions 😀

Thanks, I checked your videos but still have the problem with the bars on top and bottom.

I tested my theory on another computer, a Thinkcentre A50p, and had the following results:

1) Installed AGP GeForce FX 5700LE 128MB card without drivers and had the bars.
1) Installed AGP GeForce FX 5700LE 128MB card WITH drivers and had the bars.
3) Removed AGP card and used Integrated Intel Extreme Graphics 2 without drivers and had the bars.
4) Used Integrated Intel Extreme Graphics 2 WITH drivers and finally NO BARS! Proper fullscreen ratio stretched to all 4 corners, and no changes to the config file.

This is what I think is going on: Dosbox may not actually be designed to work with the old 4:3 screens effectively. Another factor may be hardware compatibility.
My pci-e and agp Geforce 128mb cards don't stretch to proper fullscreen, and I've tried all possible config changes (even backwards ones like 480x640 or tiny forced 4x3 which gave a tiny blue rectangle), yet my ati 256mb card works fine, also the integrated cards as I mentioned.

I guess the final result is pull the cards out of the PCs I use for Dosbox, and keep them in the PCs for other uses. It would be nice to know why this is happening.....

Personally, these settings tend to work for me, assuming the desktop resolution is 1024x768:

1fullscreen=true
2.
3.
4fullresolution=1024x768
5.
6.
7output=overlay
8.
9.
10.
11.
12aspect=true
13scaler=normal2x

You may also try ddraw (on Windows), opengl or openglnb as different values for "output". Note that the aspect correction will *not* apply in textual modes.

Yes, try different outputs as some cards may need it.

But as you've noticed with the integrated intel chip, it's also a driver issue. Most of the times sending people off to use the latest driver AND try different output modes in dosbox brings success

There should be options in the ATI and nVidia control panels to control how the screen is scaled. See 4:3 Aspect Ratios and 16:9 monitors and Distortion on 16:10 widescreen . Note that the relevant options may only appear if you're using a DVI connection.

Okay, thanks everyone. This is what's been happening:

It DOES work with fullscreen=1024x768 output=overlay aspect=true
but only if I load an actual game. I didn't want to spend time on this step so I was stuck on that vertically squished C:\ prompt screen.

Without the video cards installed the prompt screen is properly full so I'm still wondering about that.....

Anyway, I did discover something in my tests. If you want the image to look skinnier, use a wider aspect ratio. For example instead of 1280x1024 use 1240x720 (I had to keep the width below 1280) and this forces dosbox to resize and squish the overwide image. I got the idea when seeing how windows settings make everything skinnier when you choose a wider aspect ratio. With more stuff sharing the screen width it has to get skinnier to fit. So wider screen aspect = skinnier images.