Int 15 Fn D601 - Later Ps/2s - Read Boot Device Key [B]

AX = D601h
BL = 00h
DX = device ID

Return: CF clear on success
AH = 00h
CF set on error
AH = status (86h for function not supported)

See Also: AX=D600h/BL=00h,AX=D601h/BL=01h,AX=D602h