Compatibility: 4.0 only Undoc
BX drive (0=default, 1=A, 2=B, etc.)
CH 08H (device category: block device)
DS:DX addr of a 16-bit buffer to receive information
DS:DX buffer contains returned data:
DS:[DX+1] 00H=drive is NOT locked
01H=drive is locked; access is denied
Info: Obtains the current setting of the disk access flag. The driver
may disable all disk access, for instance, when it detects
unformatted media or an invalid boot record.
Note: This function is not documented in official MS-DOS references.
Fn 440dH (generic IOCTL for block devices)