INT 21 - DOS 2+ - IOCTL - SET DEVICE INFORMATION
AX = 4401h
BX = handle (must refer to character device)
DX = device information word (see AX=4400h)
(DH must be zero)
Return: CF clear if successful
CF set on error
AX = error code (01h,05h,06h,0Dh) (see AH=59h)
SeeAlso: INT 2F/AX=122Bh

See also: 214400

214401 - DOS 2+ - IOCTL - SET DEVICE INFORMATION