In the CP/M 8 bit operating system used on early personal computers, the standard DUMP program would list a file 16 bytes per line with the hex offset at the start of the line and the ASCII equivalent of each byte at the end.  Bytes outside the standard range of printable ASCII characters (20 to 7E) would be displayed as a single period for visual alignment. This same format was used to display memory when invoking the D command in the standard CP/M debugger DDT .  Later incarnations of the format (. in the DOS debugger DEBUG ) changed the space between the 8th and 9th byte to a dash without changing the overall width.