Feature request: Support for VHD dynamic hard disk images

[SiriusVI87]

Hello everyone,

after successfully setting up Dos games and Win3x games with Dos Box Pure, I wanted to do the same with Win9x games. However, even though the setup is the same, Win9x games won't launch.

Maybe someone can help point me into the right direction.

Win3x setup (working):

I use .conf files to load the games with Dos Box Pure. As an example I will show the autoexec section of the .conf file

[autoexec]
mount c .\Win3x\3DDino3x\
imgmount d .\Win3x\3DDino3x\cd\3D_DINOSAUR.ISO -t cdrom
c: 
path=C:\;z:\;c:\windows\;c:\ka\dino3d\
@cd ka\dino3d
@cls 
@win 
exit

My setup works with every game I tried.

Win9x setup (not working):

Just like with Win3x games, I use .conf files to load the games with Dos Box Pure. As an example I will show the autoexec section of the .conf file:

[autoexec]    
# Lines in this section will be run at startup.    
# You can put your MOUNT lines here.    
vhdmake -f -l .\emulators\dosbox\x98\parent/W98-C.vhd .\emulators\dosbox\x98\W98-C.vhd 
IMGMOUNT c .\emulators\dosbox\x98\W98-C.vhd    
IMGMOUNT d ".\Win9x\1994\Day at the Races (1994)\Day at the Races (1994).vhd"    
mount e ".\Win9x\1994\Day at the Races (1994)\Day at the Races v1.10.zip"    
echo off
cls
BOOT -l c    

Unfortunately, unlike with Win3x games, this won't work. Dos Box Pure will give an error message saying:

"unable to boot off of drive CC"

Is Dos Box Pure incompatible with this type of setup for Win9x games, or is there an error in the setup on my end?

Any help is appreciated, thank you!

EDIT: My previous post was deleted because of references to piracy. I wasn't aware that I was referencing piracy in any way. If I did it again here, please tell me what I should avoid mentioning. I honestly don't understand. Thank you!

[schellingb]

The chapter "Installing an Operating System" of the documentation mentions how an operating system like Windows 95 or Windows 98 can be installed in DOSBox Pure. It is done with the menu and like everything official does not require the use of .conf files at all.

If you use .conf files, you basically are using DOSBox Pure as just regular DOSBox and you might be better off asking on a DOSBox forum or consult the official DOSBox homepage or wiki.

First thing that stands out here is the call to a command vhdmake which does not exist in DOSBox (or DOSBox Pure), is this an external program? And I wonder if you are using some enhanced version of VHD files. If you check the Wikipedia article on VHD (file format) you'll see it can be all kinds of variants, but DOSBox only supports the very basic "Fixed hard disk image" type of VHD. That type is basically just a .IMG file renamed to .VHD which is a raw hard disk image. So if you're trying to mount more advanced .VHD files, DOSBox might still just mount them as a raw disk images but it won't be able to find any partitions in it and thus it won't be able to boot off of it.

My previous post was deleted because of references to piracy. I wasn't aware that I was referencing piracy in any way

Seeing that you avoided any references this time I think you know what you did or at least figured it out. GitHub is a bit annoying with this stuff because it allows me to alter the content of messages but I can't remove the title of an issue. So the only choice I have is to remove the entire issue when the reference happens to be in the issue title.

[SiriusVI87]

Thank you @schellingb for taking the time to answer!

The .conf file I use was originally designed to work with "DOSBox-X". It's possible that DOSBox-X supports the vhdmake command while dos box pure does not. Since you have confirmed this, it seems like this is pretty much the issue here.

The reason I use the .conf files at all is that they contain game-specific settings that I want to use, and for Win3x games, I believe the autoexec commands are actually necessary to start many of the games I want to launch.

I still want to use dos box pure over standard dos box, because it has save state support, which standard dos box doesn't have.

[schellingb]

Ah, yeah DOSBox-X I believe also supports some of the more advanced VHD formats. So maybe this issue should be renamed to "Feature request: Support for VHD dynamic hard disk images" because I think that's the main reason it doesn't work. Just to confirm, can you post the actual file size of your "W98-C.vhd" file you're trying to mount? Also, if possible, can you open that .VHD file in 7-Zip, press the "info" button, then select all rows and copy/paste them here?

[SiriusVI87]

Ah, yeah DOSBox-X I believe also supports some of the more advanced VHD formats. So maybe this issue should be renamed to "Feature request: Support for VHD dynamic hard disk images" because I think that's the main reason it doesn't work. Just to confirm, can you post the actual file size of your "W98-C.vhd" file you're trying to mount? Also, if possible, can you open that .VHD file in 7-Zip, press the "info" button, then select all rows and copy/paste them here?

Sure thing:

The file size is: 66,1 MB (69.357.056 bytes)

7-Zip Info reads:

Size: 266 709 209
Packed Size: 326 172 672
Folders: 178

Files: 2 892
Path: 0.fat
Type: FAT
Physical Size: 68 713 956 864
File System: FAT32
Cluster Size: 32 768
Free Space: 68 338 548 736
Headers Size: 22 656 000
Sector Size: 512
ID: 201795094
----------------:
Path: 0.fat
Size: 68 713 956 864
File System: FAT32-LBA
Offset: 32 256
Primary: +
Begin CHS: 0-1-1
End CHS: 161-254-63
------------------------:
Path: W98-C.mbr
Type: MBR
Physical Size: 68 719 476 736
Sector Size: 512
ID: 0
----------------:
Size: 68 719 476 736
Packed Size: 69 206 016
Created: 2025-12-05 11:43:09.0000000
------------------------:
Path: O:\LaunchBox\Games\Configs!win9x\1994\emulators\dosbox\x98\W98-C.vhd
Type: VHD
Physical Size: 69 357 056
Created: 2025-12-05 11:43:09.0000000
Cluster Size: 2 097 152
Method: Differencing -> Dynamic
Volumes: 2
Total Physical Size: 465 948 672
Parent: parent\W98-C.vhd
Creator Application: vbox 7.0
Host OS: Windows
Saved State: -
ID: F1626C10C30A975A0419B254B37ABE03
------------------------:
------------------------:

[DarkCTO]

Thank you @schellingb I will be watching this with great interest.
Would allow running many win98 games in zip files, with just one copy of windows 98.
@SiriusVI87 appreciate you bringing this up.

[aderumier]

The chapter "Installing an Operating System" of the documentation mentions how an operating system like Windows 95 or Windows 98 can be installed in DOSBox Pure. It is done with the menu and like everything official does not require the use of .conf files at all.

If you use .conf files, you basically are using DOSBox Pure as just regular DOSBox and you might be better off asking on a DOSBox forum or consult the official DOSBox homepage or wiki.

First thing that stands out here is the call to a command vhdmake which does not exist in DOSBox (or DOSBox Pure), is this an external program? And I wonder if you are using some enhanced version of VHD files. If you check the Wikipedia article on VHD (file format) you'll see it can be all kinds of variants, but DOSBox only supports the very basic "Fixed hard disk image" type of VHD. That type is basically just a .IMG file renamed to .VHD which is a raw hard disk image. So if you're trying to mount more advanced .VHD files, DOSBox might still just mount them as a raw disk images but it won't be able to find any partitions in it and thus it won't be able to boot off of it.

My previous post was deleted because of references to piracy. I wasn't aware that I was referencing piracy in any way

Seeing that you avoided any references this time I think you know what you did or at least figured it out. GitHub is a bit annoying with this stuff because it allows me to alter the content of messages but I can't remove the title of an issue. So the only choice I have is to remove the entire issue when the reference happens to be in the issue title.

Hi, I think this conf is coming from the new exowin9x collection. vhdmake is creating a liked clone of drive C "W98-C.vhd" file to a new other files. (the original is readonly, and the newer is like an virtual copy/overlay which use only diff).

This is a great feature to have clean drive_c for each game at each start, avoid corruption on unclean windows shutdown or .dll clash between games, without taking too much space.

It's like dosbox-pure .sav, but handled at .vhd level directly (because dosbox-X don't have the .sav overlay feature)

I'm currently looking to convert this collection to dosbox-pure too (to get it run on batocera linux distro), but I just begin to work on it.