Int 21 Fn 4451  - Concurrent DOS V3.2+ - Installation Check                [O]

   AX = 4451h

Return: CF set if not Concurrent DOS
       AX = error code (see AH=59h)
   CF clear if successful
       AH = single-user/multiuser nature
       10h single-user
           AL = operating system version ID (see AX=4452h)
       14h multiuser
           AL = operating system version ID (see below)

Notes: as of Concurrent DOS/XM 5.0 (possibly earlier), the version is stored
     in the environment variable VER
   use this function if you are looking for multiuser capabilities,
     AX=4452h for single-user
   this function should never return the single-user values

See Also: AX=4452h,AX=4459h

Values for operating system version ID:
 32h   Concurrent PC DOS 3.2
 41h   Concurrent DOS 4.1
 50h   Concurrent DOS/XM 5.0 or Concurrent DOS/386 1.1
 60h   Concurrent DOS/XM 6.0 or Concurrent DOS/386 2.0
 62h   Concurrent DOS/XM 6.2 or Concurrent DOS/386 3.0
 66h   DR Multiuser DOS 5.1
 67h   Concurrent DOS 5.1