Int 21 Fn 30  - DOS 2+ - Get Dos Version                                   [D]

   AH = 30h
---DOS 5+ ---
   AL = what to return in BH
       00h OEM number (as for DOS 2.0-4.0x)
       01h version flag

Return: AL = major version number (00h if DOS 1.x)
   AH = minor version number
   BL:CX = 24-bit user serial number (most versions do not use this)
---if DOS <5 or AL=00h---
   BH = MS-DOS OEM number (see below)
---if DOS 5+ and AL=01h---
   BH = version flag
       bit 3: DOS is in ROM
       other: reserved (0)

Notes: the OS/2 v1.x Compatibility Box returns major version 0Ah (10)
   the OS/2 v2.x Compatibility Box returns major version 14h (20)
   the Windows/NT DOS box returns version 5.00, subject to SETVER
   DOS 4.01 and 4.02 identify themselves as version 4.00; use
     INT 21/AH=87h to distinguish between the original European MS-DOS 4.0
     and the later PC-DOS 4.0x and MS-DOS 4.0x
   IBM DOS 6.1 reports its version as 6.00; use the OEM number to
     distinguish between MS-DOS 6.00 and IBM DOS 6.1 (there was never an
     IBM DOS 6.0)
   generic MS-DOS 3.30, Compaq MS-DOS 3.31, and others identify themselves
     as PC-DOS by returning OEM number 00h
   the version returned under DOS 4.0x may be modified by entries in
     the special program list (see AH=52h); the version returned under
     DOS 5+ may be modified by SETVER--use AX=3306h to get the true
     version number

See Also: AX=3000h/BX=3000h,AX=3306h,AX=4452h,AH=87h,INT 15/AX=4900h

See Also: INT 2F/AX=122Fh,INT 2F/AX=E002h

Values for DOS OEM number:
 00h   IBM
 01h   Compaq
 02h   MS Packaged Product
 04h   AT&T
 05h   Zenith
 06h   Hewlett-Packard
 0Dh   Packard-Bell
 16h   DEC
 23h   Olivetti
 29h   Toshiba
 33h   Novell (Windows/386 device IDs only)
 34h   MS Multimedia Systems (Windows/386 device IDs only)
 35h   MS Multimedia Systems (Windows/386 device IDs only)
 4Dh   Hewlett-Packard
 66h   PhysTechSoft (PTS-DOS)
 99h   General Software's Embedded DOS
 EEh   DR-DOS
 EFh   Novell DOS
 FFh   Microsoft, Phoenix