DOS box basically provides its own BIOS and DOS, so int 21h and friends are implemented by the emulator, so it can do things like redirecting access to the real

DOS box basically provides its own BIOS and DOS, so int 21h and friends are implemented by the emulator, so it can do things like redirecting access to the real file system. Windows 9x doesn’t (normally) use real mode DOS / BIOS calls for disk access, it has its own 32 bit disk drivers and file systems running in the virtual machine manager kernel (vfat.vxd and so on). So DOSbox has to do things in a far more traditional way, presenting a virtual hard disc device etc.