It is FDUBCD then.
The problem is that there are at least 3 booting systems involved, if not more. The first is either ISOLINUX or GRUB4DOS. Whichever is used, MEMDISK boots fdubcd.iso. Then the fork from NwDSK is used, and then MODBOOT.
As far as I can see, when booting with ISOLINUX, shsurdrv.exe "mounts" the image (from %ramdrv%).
When using GRUB4DOS as in UBCD511, I think a "fallback" method is used.
So, there are several possibilities to mount an additional image so FDUBCD could have access to its content. I mean, clearly the content of each image has already been expanded (otherwise the user couldn't get to use it), but the filesystem can't be used directly by DOS (FDUBCD), so no letter is assigned.
Maybe using MEMDISK with additional or different parameters (but I doubt it), or shsurdrv, or shsucdx (which, BTW, could also be updated with a newer version).
The problem is that there are at least 3 booting systems involved, if not more. The first is either ISOLINUX or GRUB4DOS. Whichever is used, MEMDISK boots fdubcd.iso. Then the fork from NwDSK is used, and then MODBOOT.
As far as I can see, when booting with ISOLINUX, shsurdrv.exe "mounts" the image (from %ramdrv%).
When using GRUB4DOS as in UBCD511, I think a "fallback" method is used.
So, there are several possibilities to mount an additional image so FDUBCD could have access to its content. I mean, clearly the content of each image has already been expanded (otherwise the user couldn't get to use it), but the filesystem can't be used directly by DOS (FDUBCD), so no letter is assigned.
Maybe using MEMDISK with additional or different parameters (but I doubt it), or shsurdrv, or shsucdx (which, BTW, could also be updated with a newer version).