Int 21 Fn 4452  - Dr-dos 3.41+ - Determine DOS Type/get Dr-dos Version     [O]

   AX = 4452h ("DR")
   CF set

Return: CF set if not DR-DOS
       AX = error code (see AH=59h)
   CF clear if DR-DOS
       DX = AX = version code
       AH = single-user/multiuser nature
       10h single-user
           AL = operating system version ID (see below)
       14h multiuser
           AL = operating system version ID (see AX=4451h)

Notes: the DR-DOS version is stored in the environment variable VER
   use this function if looking for single-user capabilities, AX=4451h
     if looking for multiuser; this call should never return multiuser
     values

See Also: AX=4412h,AX=4451h,AX=4459h

Values for operating system version ID:
 60h   DOS Plus
 63h   DR-DOS 3.41
 64h   DR-DOS 3.42
 65h   DR-DOS 5.00
 67h   DR-DOS 6.00
 70h   PalmDOS
 71h   DR-DOS 6.0 March 1993 "business update"
 72h   Novell DOS 7.0