IBM PC mode, drive A: and B: should always exist even if nothing mounted to it

[joncampbell123]

Is your feature request related to a problem? Please describe.

No response

What you want

As real MS-DOS does, DOSBox-X should always provide a drive A: and B: even if nothing is mounted there. Like real MS-DOS, the A: and B: drives should present a drive letter that always reports "medium not found" when nothing has been mounted there.

Of course there will be a dosbox.conf option to enable/disable this.

Describe alternatives you've considered

No response

Additional information

This is related to a demoscene entry that was found to use the INT 13h drive A: interception trick (needing -int13 to make it work), except that it won't do the trick if either drive A: doesn't exist, or if drive A: has a valid mounted filesystem. The demo appears to require a valid drive A: with no disk in the drive.

Have you checked that no similar feature request(s) exist?

• I have searched and didn't find any similar feature request.

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[joncampbell123]

This mode should not apply to PC-98 mode. I'm not aware of any PC-98 software that requires such hackery, and usually on PC-98 systems, drive A: is the boot drive, not necessarily a floppy drive. On such systems, Windows 95 can be seen running software from A:¥Program Files and A:¥Windows for example.

[joncampbell123]

Perhaps the way this should be done so that it's consistent with INT 13h is that the "no medium found" drives are INT 13h devices that always return that, then the DOS layer presents these as drive A: and B:.

At the same time if done as INT 13h, the guest OS can see these floppy drives with no media in them as well.

[joncampbell123]

Actually:

bios_disk INT 13h floppy device (C++ class) that always returns "medium not found".

IMGMOUNT should interpret a filename of "none" to mean an INT 13h drive (and maybe a drive letter) that returns "medium not found". That way you can swap disk to simulate inserting a disk into an empty drive, and removing it later, etc.

The DOS kernel, if instructed by dosbox.conf, could automatically set up A: and B: with the "medium not found" disk image. In that case, IMIGMOUNT could be coded so that if asked to mount a disk image over it, it will first unmount the "medium not found" image to then mount the requested image, so existing dosbox.conf files don't break. Likewise, unmounting a floppy disk image would return the drive to the "medium not found" handler. Only if dosbox.conf says so.

This would also allow presenting an empty floppy drive to a guest OS.

EDIT: imageDiskEmptyDrive already exists

[joncampbell123]

For this to work, the FAT driver needs to check BPB change and "unformatted" change (update the unformatted flag) so that the transition to "medium not found" to valid filesystem works properly and A: can function properly.