AH = 0D DL = fixed drive number (80h=drive 0, 81h=drive 1) on return: AH = status (see INT 13,STATUS) CF = 0 if successful = 1 if error - 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 - used to force drive recalibration similar to INT 13,0 - drive heads are positioned at track zero