Who Invented the Dot in Filenames?

Who invented the dot (“.”) that precedes the file type extension, as in document.doc or metal.mp3? As we near the end of what has emerged as a most interesting year, we all could use the diversion of examining the history of something so simple and pervasive, that we all take for granted.

A note from my friend Brad Templeton reminded me that being in the right place at the right time can be profound. In fact, as strange as it sounds, Brad Templeton may well have invented the dot in “.com“, as he discusses here. As he says:

Brad Templeton
Brad Templeton

“Indeed if it was me, it was simply by virtue of the fact that having been around at the beginning of these things, and taking an interest in these issues. Being in the right place at the right time. But it’s simultaneously mind-boggling, conceit-building and humbling to think that what I said might have sparked something that became so universal.”

This led me to ask myself, who orginated the ubiquitous dot that separates the extension, denoting file type, from the base file name. A much older concept, clearly the use of dot as an internet name separator was influenced, perhaps subconciously, from the longstanding filenaming convention.

The Windows filenames of today are direct descendents of MS-DOS which lacked tree-structured directories and restricted filenames to an 8.3 format, consisting of a maximum of 8 characters of base filename followed by up to 3 characters of an extension connoting the type of data stored in the file. MS-DOS, in turn, directly inherited this convention from CP/M, and indirectly from the UNIX family of operating systems.

I have directly worked with all of the above systems since their early days, but to go back further, I must rely on the oral history I was hearing at the time. CP/M was directly inspired by the Digital Equipment Corporation family of operating systems such as DOS-11 and RSX-11. The dot convention may well have been inherited via TOPS-10 for the DEC PDP-10 line of computers. Can anyone please confirm or deny this? At the very least, the 3 letter limitation of extension length, still common today, came from those systems which stored the extension in a 16-bit word in a format known as RAD50.

However, filename extensions separated by a dot were also a feature of Multics, which dates back to 1964.

Thus it is unclear to me whether Multics or DEC operating systems were the true originator of this concept, or whether there is an even older, perhaps common, ancestor. Can an alert reader, possibly a computing pioneer, help enlighten us on this important question.

Happy New Year to all. Wishing you all a happy and prosperous 2009.

Happy New Year - 2009!