INT 13,A - Read Long Sector (XT & newer)

	AH = 0A
	AL = number of sectors	(1-121 dec.)
	CH = track number  (0-1023 dec., see below)
	CL = sector number  (1-17 dec., see below)
	DH = head number  (0-15 dec.)
	DL = fixed drive number  (80h=drive 0, 81h=drive 1)
	ES:BX = address of buffer


	on return:
	AH = status  (see INT 13,STATUS)
	AL = number of sectors actually transferred
	CF = 0 if successful
	   = 1 if error


	- BIOS disk reads should be retried at least three times and the
	  controller should be reset upon error detection
	- many good programming references indicate this function is only
	  available on the AT, PS/2 and later systems, but all hard disk
	  systems since the XT have this function available
	- reads regular data sectors (128-1024 bytes) with an additional
	  4 byte ECC code included
	- a DMA boundary error will occur if the buffer at ES:BX crosses
	  a 64K segment boundary
	- only the disk number is checked for validity
	- the parameters in CX change depending on the number of cylinders;
	  the track/cylinder number is a 10 bit value taken from the 2 high
	  order bits of CL and the 8 bits in CH (low order 8 bits of track):

	  │F│E│D│C│B│A│9│8│7│6│5│4│3│2│1│0│  CX
	   │ │ │ │ │ │ │ │ │ │ └─┴─┴─┴─┴─┴────	sector number
	   │ │ │ │ │ │ │ │ └─┴────────────  high order 2 bits of track number
	   └─┴─┴─┴─┴─┴─┴─┴────────────	low order 8 bits of track number

	- see	INT 13,2