Function 1Ah	ESDI Hard Disk - Format 			(PS/2)
entry   AH      1Ah 
	AL      defect table count 
	CL      format modifiers 
		bits    0 ignore primary defect map 
			1 ignore secondary defect map 
			2 update secondary defect map 
			3 perform surface analysis 
			4 generate periodic interrupt 
	DL      drive 
	ES:BX   pointer to defect table 
return  CF      set on error 
		AH	status (see Int\13f\01)
note	If periodic interrupt selected, Int\15f\0F is called after each
        cylinder is formatted