INT 21 U - AI Architects - OS/x86??? - API
        AX = 4403h
        BX = handle for device "AIA_OS"
        CX = number of bytes to write (ignored)
        DS:DX -> 12-byte buffer, first byte is command:
                        81h installation check
                        82h get API entry point
                        84h uninstall
Return: CF clear if successful
            AX = number of bytes actually written
        CF set on error
            AX = error code (01h,05h,06h,0Ch,0Dh) (see AH=59h)
Notes:  these functions are only available if the DOS extender was loaded as a
          device driver in CONFIG.SYS
        called by TKERNEL (a licensed version of AI Architects/Ergo OS/x86)
SeeAlso: INT 2F/AX=FBA1h/BX=0081h,INT 2F/AX=FBA1h/BX=0082h
Index:  installation check;OS/x86|entry point;OS/x86|uninstall;OS/x86

Format of buffer on return:
Offset  Size    Description
 00h  4 BYTEs   signature "IABH"
---if func 81h---
 (no additional fields)
---if func 82h---
 04h    DWORD   pointer to API entry point (see INT 2F/AX=FBA1h/BX=0082h)
---if func 84h---
 04h    WORD    success indicator
 06h    WORD    segment of ???
 08h    WORD    segment of ??? memory block to free if nonzero
 0Ah    WORD    segment of ??? memory block to free if nonzero

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