Editing Hex dump (section)

==DUMP, DDT and DEBUG==
In the [[CP/M]] 8-bit operating system used on early personal computers, the standard [[DUMP (CP/M command)|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.<ref name="DR_CPM22"/>{{rp|pages=((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 same format was used to display memory when invoking the D command in the standard CP/M [[debugger]] [[DDT (CP/M command)|DDT]].<ref name="DR_CPM22"/>{{rp|page=4-5}} Later incarnations of the format (e.g. in the DOS debugger [[DEBUG (DOS command)|DEBUG]]) changed the space between the 8th and 9th byte to a dash, without changing the overall width.

This notation has been retained in operating systems that were directly or indirectly derived from CP/M, including [[DR-DOS]], [[MS-DOS]]/[[PC&nbsp;DOS]], [[OS/2]] and [[Windows]]. On Linux systems, the command hexcat produces this classic output format, too. 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.

<syntaxhighlight lang="hexdump">
1234:0000: 57 69 6B 69 70 65 64 69 61 2C 20 74 68 65 20 66  Wikipedia, the f
1234:0010: 72 65 65 20 65 6E 63 79 63 6C 6F 70 65 64 69 61  ree encyclopedia
1234:0020: 20 74 68 61 74 20 61 6E 79 6F 6E 65 20 63 61 6E   that anyone can
1234:0030: 20 65 64 69 74 00 00 00 00 00 00 00 00 00 00 00   edit...........
</syntaxhighlight>

Here the leftmost column represents the address at which the bytes represented by the following columns are located. CP/M and various [[DOS]] systems ran in [[real mode]] on the [[x86]] [[CPU]]s, where addresses are composed of two parts (base and offset).

In the above examples the final 00s are non-existent bytes beyond the end of the file. 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.:
<syntaxhighlight lang="hexdump">
1234:0000: 57 69 6B 69 70 65 64 69 61 2C 20 74 68 65 20 66  Wikipedia, the f
1234:0010: 72 65 65 20 65 6E 63 79 63 6C 6F 70 65 64 69 61  ree encyclopedia
1234:0020: 20 74 68 61 74 20 61 6E 79 6F 6E 65 20 63 61 6E   that anyone can
1234:0030: 20 65 64 69 74                                    edit           
</syntaxhighlight>

or
<syntaxhighlight lang="hexdump">
1234:0000: 57 69 6B 69 70 65 64 69 61 2C 20 74 68 65 20 66  Wikipedia, the f
1234:0010: 72 65 65 20 65 6E 63 79 63 6C 6F 70 65 64 69 61  ree encyclopedia
1234:0020: 20 74 68 61 74 20 61 6E 79 6F 6E 65 20 63 61 6E   that anyone can
1234:0030: 20 65 64 69 74 ** ** ** ** ** ** ** ** ** ** **   edit           
</syntaxhighlight>