AH = 1C DL = drive number (0 for default, 1 = A:, Z: = 26) on return: AL = sectors per cluster CX = bytes per sector DX = clusters on disk DS:BX = pointer to Media Descriptor Byte found in FAT - retrieves information on capacity and format of specified drive - DS:BX can be used to determine if drive is RAMDISK or removable - see INT 21,1B