INT 13,7 - Format Drive Starting at Specified Track (XT & portable)

	AH = 07
	AL = interleave value (XT only)
	BX = format buffer, size = 512 bytes;  the first 2*(sectors/track)
	     bytes contain F, N for each sector where:

		F = 00h for good sector
		F = 80h for bad sector
		N = sector number

	on return:
	AH = status  (see INT 13,STATUS)
	CF = 0 if successful
	   = 1 if error


	- BIOS disk write attempts should reset the controller on error
	- only the disk number is checked for validity