INT 2F - 4DOS.COM v2.1+ - API(Application Program[ming] Interface) The defined set of calls which a program may make to interact with or request services of the operating system or environment under which it is running.  Because the inputs and outputs of the calls are well-defined, a program using the API can continue using the identical calls even if the internal organization of the program providing the API changes.
	AX = D44Dh
	BH = function
	    00h installation check
		Return: AX = 44DDh
			BL = major version number
			BH = minor version number
			CX = PSPsee Program Segment Prefix segment address for current invocation
			DL = 4DOS shell number (0 for the first (root) shell,
			      updated each time a new copy is loaded)
	    01h (internal, v2.1-3.03) terminate current copy of 4DOS
		Return: nothing
		(internal, v4.0+) ???
		Return: AX = 44DDh
			ES:BX -> data area (see #03086)
	    02h ???
		DX = ???
		Note:	v5.52 signals "unrecoverable error" and then terminates
			  with INT 21/AH=4Ch or enters a deliberate infinite
			  loop if ???
	---v2.1-3.03 only---
	    03h EXEC program
		CX:DX -> EXEC record (see #03087)
	    FEh deallocate shell number (passed through to root shell)
		???
	    FFh allocate shell number (passed through to root shell)
	---v5.52---
	    03h get ???
		BL = ??? (00h/01h)
		Return: DX = current value of ???
	    04h set ???
		BL = ??? (00h/01h)
		DX = new value for ???
Note:	a bug in v3.00 will crash the system if unrecognized value in BH
SeeAlso: AX=D44Eh,AX=D44Fh/BX=0000h,AX=E44Dh,INT 21/AX=4403h"DOS"
SeeAlso: INT 14/AX=7000h
Index:	installation check;4DOS|installation check;NDOS


Format of 4DOS v4.0 data area:
Offset	Size	Description	(Table 03086)
 00h  2 BYTEs	???
 06h	WORD	XMSsee Extended Memory Specification handle for swapping
	???
SeeAlso: #03087


Format of 4DOS EXEC v2.1-v3.03 record:
Offset	Size	Description	(Table 03087)
 00h	WORD	offset of ASCIZA NUL-terminated ASCII string.	The ASCIZ string "ABC" consists of the four bytes 41h, 42h, 43h, and 00h.  Unless otherwise specified, maximum lengths given in the interrupt list do not include the terminating NUL. program name in same segment as EXEC record
 02h	WORD	offset of DOS commandline in same segment as EXEC record
 04h	WORD	segment of environment for child process (see INT 21/AH=26h)
SeeAlso: #03086