INT 21,2F - Get Disk Transfer Address (DTA)

	AH = 2F

	on return:
	ES:BX = pointer to current DTA

	- returns the DTA address
	- the default DTA is a 128 byte block at address 80h in the
	  Program Segment Prefix (PSP).  This area also contains the
	  command tail at program startup it must be saved or the DTA
	  must be relocated before use to preserve the command tail

	- see	INT 21,1A