Logical filename formats tends to depend upon the specific device addressed. The most common device used, of course, is the floppy disk system, which uses a format similar to codice_12, where M is a flag of sorts ($ for directory listing, @ for indicating a desire to overwrite a file if it already exists, unused otherwise.), D is the (optional) physical disk unit number (0: or 1: for dual-drive systems, just 0: for single-disk units like the 1541, et al., which defaults to 0: if left unspecified), codice_13 is a resource name up to 16 characters in length (most characters allowed except for certain special characters), and codice_14 is an optional comma-separated list of attributes or flags. For example, if the user wants to overwrite a program file called codice_15, they might see a filename like codice_16 used in conjunction with device 8 or 9. Meanwhile, a filename for the RS-232 driver (device 2) consists simply of four characters, encoded in binary format.