It's an unfortunate side effect of software development that, as time passes, new versions of the software will need to be released1. This means that there will inevitably come a time where you need to work out which version of a given piece of software you actually have. There are a number of approaches out there to make it easier for the end-user to work out which version of something they have, but unfortunately pretty much none of them can be used for .osm files.
However, each .osm file contains a 'Windows Resource' block; a chunk of data that, among other things, stores the version information.
Unfortunately, .osm files, and the windows resource data within them, are not human-readable. In order to find out which version of a .osm file you are looking at, you need to use a resource viewer or editor. One very easy to use example of this is called Anolis Resourcer.
Download Anolis Resourcer by clicking the "download" link on the page linked above.
Unzip the archive you have downloaded.
Run the Resourcer.exe
program.
Click 'Open' in the toolbar.
In the file requester, change the file filter to All Files (*.*)
Locate the .osm file you want to obtain the version of and click 'Open'
In the left part of the Anolis Resourcer window you should now see the name
of the .osm file with a + - 1.0 Version
line below it.
Click on the +
to open the next level, you should now see a line with
+ - 1
on it. Click on the 1
and the right side of the window should
show the version information, something like that shown here:
In the version information you can see String - FileVersion
; that's the
version of the .osm file you've opened.
If this doesn't happen, it means that the software has been abandoned. ↩