INT 21,1A - Set Disk Transfer Address (DTA)

	AH = 1A
	DS:DX = pointer to disk transfer address (DTA)

	returns nothing

	- specifies the disk transfer address to DOS
	- DTA cannot overlap 64K segment boundary
	- offset 80h in the PSP is a 128 byte default DTA supplied
	  by DOS upon program load
	- use of the DTA provided by DOS will result in the loss
	  of the program command tail which also occupies the 128
	  bytes starting at offset 80h of the PSP
	- see	INT 21,2F