A:-)Brunuś
asks why
NTVDM creates empty IO.SYS and MSDOS.SYS
every time it starts up.
For compatibility, of course.
Specifically, it was added for one particular program
that searched for the MS-DOS system files,
and if they are missing,
it got confused and corrupted your CONFIG.SYS file.
This reminds me of another program we discovered in Windows 95
that parsed your SYSTEM.INI file,
and if any line in that file was longer than 80 characters,
it deleted your
SYSTEM.INI file outright.
That'll teach ya.