INT 2F - MS Windows - "DOSMGR" VIRTUAL DEVICE API
        AX = 1607h
        BX = 0015h (VxD identifier of "DOSMGR")
        CX = function
            0000h query instance processing
                DX = 0000h
                Return: CX = state
                            0000h not instanced
                            other instanced (DOS 5+ kernel returns 0001h)
                                DX = segment of DOS drivers or 0000h for
                                        default of 0070h
                                ES:BX -> patch table (see below)
            0001h set patches in DOS
                DX = bit mask of patch requests
                    bit 0 enable critical sections
                    bit 1 NOP setting/checking user ID
                    bit 2 turn INT 21/AH=3Fh on STDIN into polling loop
                    bit 3 trap stack fault in "SYSINIT" to WIN386
                    bit 4 BIOS patch to trap "Insert disk X:" to WIN386
                Return: AX = B97Ch
                        BX = bit mask of patches applied
                        DX = A2ABh
            0002h remove patches in DOS (ignored by DOS 5.0 kernel)
                DX = bit mask of patch requests (see function 0001h)
            0003h get size of DOS data structures
                DX = bit mask of request (only one bit can be set)
                    bit 0: Current Directory Structure size
                Return: if supported request:
                            AX = B97Ch
                            CX = size in bytes of requested structure
                            DX = A2ABh
                        else:
                            all registers preserved
            0004h determine instanced data structures
                Return: AX = B97Ch if supported
                        DX = A2ABh if supported (DOS 5+ kernel returns 0000h)
                        BX = bit mask of instanced items
                            bit 0: CDS
                            bit 1: SFT
                            bit 2: device list
                            bit 3: DOS swappable data area
            0005h get device driver size
                ES = segment of device driver
                Return: DX:AX = 0000h:0000h on error (not dev. driver segment)
                        DX:AX = A2ABh:B97Ch if successful
                            BX:CX = size of device driver in bytes
Notes:  DOSMGR (DOS Manager) will check whether the OEM DOS/BIOS data has
          been instanced via this API and will not perform its own default
          instancing of the normal DOS/BIOS data if so; if this API is not
          supported, DOSMGR will also try to access instancing data through
          INT 2F/AX=1603h
        these functions are supported by the DOS 5+ kernel; DOSMGR contains
          tables of instancing information for earlier versions of DOS
        see Geoff Chappell's book _DOS_Internals_ for additional discussions of
          DOSMGR's behavior and instancing in general
SeeAlso: AX=1603h,AX=1605h,AX=1607h/BX=000Ch,AX=1607h/BX=0014h,AX=1684h

Format of patch table:
Offset  Size    Description
 00h  2 BYTEs   DOS version (major, minor)
 02h    WORD    offset in DOS data segment of "SAVEDS"
 04h    WORD    offset in DOS data segment of "SAVEBX"
 06h    WORD    offset in DOS data segment of InDOS flag
 08h    WORD    offset in DOS data segment of User ID word
 0Ah    WORD    offset in DOS data segment of "CritPatch" table to enable
                critical section calls (see INT 2A/AH=80h)
 0Ch    WORD    (DOS 5+ only) offset in DOS data segment of "UMB_HEAD",
                containing segment of last MCB in conventional memory

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