[3]: 1-41, 5-40–5-46 Bytes outside the standard range of printable ASCII characters (20 to 7E) would be displayed as a single period for visual alignment.
This notation has been retained in operating systems that were directly or indirectly derived from CP/M, including DR-DOS, MS-DOS/PC DOS, OS/2 and Windows.
The main reason for the design of this format is that it fits the maximum amount of data on a standard 80-character-wide screen or printer, while still being very easy to read and skim visually.
CP/M and various DOS systems ran in real mode on the x86 CPUs, where addresses are composed of two parts (base and offset).
Some dump tools display other characters so that it is clear they are beyond the end of the file, typically using spaces or asterisks, e.g.: or