system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: File names. Why can't Microsoft Office save or open files that have slashes or colons in their names?

Sorry - more questions!

* Why can't Microsoft Office save or open files that have slashes or colons in their names?

* Why can I *rename* a file to something like "30/60.doc," which makes it un-openable, but then when I rename it back to "30 60.doc," it suddenly opens?

* What is the benefit of saving a file with underscores instead of spaces? i.e. My_Awesome_Song.mp3 instead of My Awesome Song.mp3?

Thanks!
gpt
Slashes and colons are used as part of the *file system*; that is, the thing that tells the computer where to look for a file with that name. The Windows OS has been updated to distinguish between a slash in a filename and a "meaningful" slash, but MS Office has not.

Before things like Windows and Macs existed, you had to make a computer do things by just typing commands. Spaces were "meaningful" when you typed in those commands, so it was impossible to have a filename with spaces in it. Because of that, some very old programs cannot handle filenames with spaces.