Resolution change problems with MS-DOS in full-screen

Discussions about using non Windows and Linux guests such as FreeBSD, DOS, OS/2, OpenBSD, etc.
Post Reply
Robert Berlansky
Posts: 1
Joined: 25. May 2020, 21:41

Resolution change problems with MS-DOS in full-screen

Post by Robert Berlansky »

HOST physical machine: Windows 7 x86; AMD A8-series APU; VirtualBox 5.2.40
GUEST virtual machine: MS-DOS 6.22; 16MB RAM; 8MB VRAM

I would like to get a nice full-screen DOS session going with VBox. To get a better visual experience I've found that switching host display resolution to 640x480, before launching VBox, has MS-DOS fill the screen nearly perfect without pillar-boxing. But this isn't quite perfect because the right side of the display always runs off the screen. This isn't a matter of it being centered since the left side is completely within the display area and horizontal compensation on my monitor causes the left side to get cut-off as more from the right shifts into view. It just seems that VBox thinks that 640x480 fits an area larger than it really does, effectively lobbing off the video at one end. This happens at the command prompt as soon as DOS is loaded, and also when running any applications within the VM. I've tried quite a bit to try and rectify the problem: Changing colour depths on the host, enabling and disabling GPU scaling with different settings (i.e. Preserve Aspect, Center, Full/Stretch), toggling the hardware virtualisation settings of VBox; booting DOS clean; loading ANSI.SYS; executing MODE CON COLS=80 LINES=25; all with no effect whatsoever. This simply does not appear to be a problem with any of our other emulators in use.
I've run out of ideas, and Scale Mode just doesn't look the way I'd like it to. There must be something I've missed here. It can't be difficult for VBox to show DOS correctly in full-screen after host sets 640x480...After all, that is the basic VGA resolution! Any suggestions?
mpack
Site Moderator
Posts: 39156
Joined: 4. Sep 2008, 17:09
Primary OS: MS Windows 10
VBox Version: PUEL
Guest OSses: Mostly XP

Re: Resolution change problems with MS-DOS in full-screen

Post by mpack »

Check out View|Scaled mode in a running VM. Enable it, then drag the window to the size you want.

It must be said: you don't seem to appreciate that DOS doesn't use pixels, it sent text directly to the display card. You are limited to the text display modes supported by the display section of the BIOS, which match what was typically available back in the day, and e.g. would not have an embedded font capable of looking good when blown up on a modern display.

So check out scale mode, but don't expect a sharp font. If you want modern results, use a modern OS!
Post Reply