Int 21 Fn 2E  - Dos 1+ - Set Verify Flag                                   [D]

   AH = 2Eh
   DL = 00h (DOS 1.x/2.x only)
   AL = new state of verify flag
       00h off
       01h on

Notes: default state at system boot is OFF
   when ON, all disk writes are verified provided the device driver
     supports read-after-write verification

See Also: AH=54h