IOCTL - I/O Control for Devices

 INT 21h, 4400h  Get device information
 INT 21h, 4401h  Set device information
 INT 21h, 4402h  Read from character device
 INT 21h, 4403h  Write to character device
 INT 21h, 4404h  Read from block device
 INT 21h, 4405h  Write block device control string
 INT 21h, 4406h  Get Input status
 INT 21h, 4407h  Get Output status
 INT 21h, 4408h  Determine if a block device is removable           (DOS 3.0)
 INT 21h, 4409h  Determine if a logical device is local or remote   (DOS 3.1)
 INT 21h, 440Ah  Determine if a handle is local or remote           (DOS 3.1)
 INT 21h, 440Bh  Change sharing retry count                         (DOS 3.0)
 INT 21h, 440Ch  Issue handle generic IOCTL request                 (DOS 4.0)
 INT 21h, 440Dh  Issue block device generic IOCTL request           (DOS 3.2)
 INT 21h, 440Eh  Get logical drive                                  (DOS 3.2)
 INT 21h, 440Fh  Set logical drive                                  (DOS 3.2)