Int 21H, AH=37H, AL=01H

2 and higher

SET SWITCH CHARACTER

      AX = 3701h
      DL = new switch character

AL = status

          00h successful
          FFh unsupported subfunction

documented in some OEM versions of some releases of DOS; DOS 2.x had

        a SWITCHAR=c setting in CONFIG.SYS
      supported by OS/2 compatibility box and Novell DOS 7
      ignored by MS-DOS 5+ and DR DOS 3.41-6.0; DR DOS 6.0 and Novell DOS 7
        leave AX unchanged

AX=3700h

Text based on Ralf Brown Interrupt List Release 61