INT 13 - HARD DISK - WRITE SECTOR BUFFER (XTIBM PC XT only)
	AH = 0Fh
	DL = drive number (80h = first, 81h = second hard disk)
	ES:BX -> buffer
Return: CF set on error
	CF clear if successful
	AH = status code (see #00234)
Notes:	does not write data to the drive
	should be called before formatting to initialize an XT-type
	  controller's sector buffer
	used for diagnostics only on PS/2IBM PS/2, any model systems
SeeAlso: AH=0Bh