INT 2F - DOS v5.0 TASK SWITCHER - INSTALLATION CHECK
        AX = 4B02h
        BX = 0000h
        ES:DI = 0000h:0000h
Return: ES:DI = 0000h:0000h if task switcher not loaded
        ES:DI -> task switcher entry point (see below) if loaded
            AX = 0000h
Note:   the returned entry point is that for the most-recently loaded task
          switcher; the entry points for prior task switchers may be determined
          with the "get version" call (see below)
SeeAlso: AX=4B03h

Call task switcher entry point with:
        AX = 0000h get version
                Return: CF clear if successful
                            AX = 0000h
                            ES:BX -> task switcher version struct (see below)
                        CF set if unsupported function
        AX = 0001h test memory region
                ES:DI -> first byte to be tested
                CX = size of region to test
                Return: CF clear if successful
                            AX = memory type of tested region
                                0000h global
                                0001h global and local
                                0002h local (replaced on session switch)
                        CF set if unsupported function
        AX = 0002h suspend switcher
                ES:DI -> new task switcher's entry point
                Return: CF clear if successful
                            AX = state
                                0000h switcher has been suspended
                                0001h switcher not suspended, new switcher must
                                        abort
                                0002h switcher not suspended, but new switcher
                                        may run anyway
                        CF set if unsupported function
        AX = 0003h resume switcher
                ES:DI -> new task switcher's entry point
                Return: CF clear if successful
                            AX = 0000h
                        CF set if unsupported function
        AX = 0004h hook notification chain
                ES:DI -> callback info structure to be added to chain
                        (see AX=4B01h)
                Return: CF clear if successful
                            AX = 0000h
                        CF set if unsupported function
        AX = 0005h unhook notification chain
                ES:DI -> callback info structure to be removed from chain
                        (see AX=4B01h)
                Return: CF clear if successful
                            AX = 0000h
                        CF set if unsupported function
        AX = 0006h query API support
                BX = asynchronous API identifier
                Return: CF clear if successful
                            AX = 0000h
                            ES:BX -> API info structure (see below) for the
                                        client which provides the highest
                                        level of
                        CF set if unsupported function

Format of task switcher version structure:
Offset  Size    Description
 00h    WORD    major version of supported protocol  (current protocol is 1.0)
 02h    WORD    minor version of supported protocol
 04h    WORD    major version of task switcher
 06h    WORD    minor version of task switcher
 08h    WORD    task switcher ID (see AX=4B03h)
 0Ah    WORD    operation flags
                bit 0: set if task switcher disabled
                bits 1-15: reserved (0)
 0Ch    DWORD   pointer to ASCIZ task switcher name
                ("MS-DOS Shell Task Switcher" for DOSSHELL task switcher)
 10h    DWORD   pointer to previous task switcher's entry point or 0000h:0000h

Format of API info structure:
Offset  Size    Description
 00h    WORD    size of structure in bytes (000Ah)
 02h    WORD    API identifier
                0001h NetBIOS
                0002h 802.2
                0003h TCP/IP
                0004h LAN Manager named pipes
                0005h Novell NetWare IPX
 04h    WORD    major version \ of highest version of API for which the support
 06h    WORD    minor version / level specified in the next field is provided
 08h    WORD    support level
                0001h minimal support
                0002h API-level support
                0003h switcher compatibility
                0004h seamless compatibility