Format of buffer on return:
Offset	Size	Description	)
 00h  4 BYTEs	signature "IABH"
---if function 81h---
 (no additional fields)
---if function 82h---
 04h	DWORD	pointer to API entry point (see INT 2F/AX=FBA1h/BX=0082h)
---if function 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