INT 21 - DOS 2+ - GET DOS VERSION
AH = 30h
---DOS 5.0---
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 = OEM number
00h IBM
05h Zenith
16h DEC
23h Olivetti
29h Toshiba
4Dh Hewlett-Packard
99h STARLITE architecture (OEM DOS, NETWORK DOS, SMP DOS)
FFh Microsoft, Phoenix
---if DOS 5.0 and AL=01h---
BH = version flag
08h DOS is in ROM
10h DOS is in HMA
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 major version 1Eh (30)
DOS 4.01 and 4.02 identify themselves as version 4.00; use
INT 21/AH=87h to distinguish between the original European MSDOS 4.00
and the later PCDOS 4.0x and MSDOS 4.0x
generic MSDOS 3.30, Compaq MSDOS 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 5.0 may be modified by SETVER; use
AX=3306h to get the true version number
SeeAlso: AX=3306h,AX=4452h,AH=87h,INT 15/AX=4900h

See also: 213000

2130 - DOS 2+ - GET DOS VERSION