INT 13,1A - Format Unit (PS/2 model 50+)

	AH = 1Ah
	AL = defect table count
	DL = drive number (0=A:, 1=2nd floppy, 80h=drive 0, 81h=drive 1)
	ES:BX = far pointer to defect table
	CL = modifier bits

		|7|6|5|4|3|2|1|0|  Format Unit Modifier Bits
		 | | | | | | | `---- 1=ignore primary defect map, 0=use map
		 | | | | | | `----- 1=ignore secondary defect map, 0=use map
		 | | | | | `------ 1=update secondary defect map, 0=don't
		 | | | | `------- 1=do extended surface analysis, 0=don't
		 | | | `-------- 1=periodic interrupt status on, 0=off
		 `------------- reserved

	returns nothing

	- only the disk number is checked for validity
	- see	INT 13,STATUS