Windows detection services:

In XP all these functions return the value in AX indicating there is no
support for old windows/dos programs. It also seems that XP does not
process Int2F anymore, and does not return values for some Int21 functions.

--------W-2F1600-----------------------------
INT 2F - MS Windows - WINDOWS ENHANCED MODE INSTALLATION CHECK
	AX = 1600h
Return: AL = status
	    00h neither Windows 3.x enhanced mode nor Windows/386 2.x running
	    01h Windows/386 2.x running
	    80h XMS version 1 driver installed (neither Windows 3.x enhanced
		  mode nor Windows/386 2.x running) (obsolete--see note)
	    FFh Windows/386 2.x running
	AL = anything else
	    AL = Windows major version number >= 3
	    AH = Windows minor version number
Notes:	INT 2F/AH=16h comprises an API for non-Windows programs (DOS device
	  drivers, TSRs, and applications) to cooperate with multitasking
	  Windows/386 2.x and Windows 3.x and higher enhanced mode.
	certain calls are also supported in the Microsoft 80286 DOS extender in
	  Windows standard mode
	this function served as the installation check and AX=1610h served to
	  get the driver entry point for XMS version 1, which is now obsolete.
	  Use AX=4300h and AX=4310h instead
	Windows95 reports version 4.00, Windows95B reports version 4.03
SeeAlso: AX=160Ah,AX=1610h,AX=4300h,AX=4680h
Index:	installation check;XMS version 1
--------W-2F160A-----------------------------
INT 2F - MS Windows 3.1 - IDENTIFY WINDOWS VERSION AND TYPE
	AX = 160Ah
Return: AX = 0000h if call supported
	    BX = version (BH=major, BL=minor)
	    CX = mode (0002h = standard, 0003h = enhanced)
Note:	Windows95 reports version 4.00, Windows95B reports version 4.03
SeeAlso: AX=1600h,AX=4680h
--------W-2F4680-----------------------------
INT 2F U - MS Windows v3.0 - INSTALLATION CHECK
	AX = 4680h
Return: AX = result
	    0000h MS Windows 3.0 running in real (/R) or standard (/S) mode,
		  or DOS 5 DOSSHELL active
	    nonzero  no Windows, Windows prior to 3.0, or Windows3 in enhanced
		  mode
Note:	Windows 3.1 finally provides an installation check which works in all
	  modes (see AX=160Ah)
SeeAlso: AX=1600h,AX=160Ah
--------D-2F4A33-----------------------------
INT 2F - Windows95 - CHECK MS-DOS VERSION 7
	AX = 4A33h
Return: AX = 0000h for MS-DOS 7.00+
	    (officially) BX,DX,SI,DS may be destroyed
	    (undoc) DS:DX -> ASCIZ primary shell executable name
	    (undoc) DS:SI -> CONFIG.SYS SHELL= command line (counted string)
	    (undoc) BH = ??? (0000h)
	    (undoc) BL = ??? (0000h)
	AX nonzero (usually 4A33h) if MS-DOS 6- or other DOS
SeeAlso: AX=1611h,INT 21/AH=30h
