The magical power of extensions actually predates MS-DOS -- both CP/M and TRSDOS did the same thing in the late 70s, and I'm pretty sure both of those were insp

The magical power of extensions actually predates MS-DOS -- both CP/M and TRSDOS did the same thing in the late 70s, and I'm pretty sure both of those were inspired by mainframe operating systems. (I was a TRS-80 kid, and didn't know until much later why our equivalent of batch files had the extension "JCL".) Having said that, though, we could at least wish that some variant of the Mac's old idea of separate creator and document codes stored as metadata had caught on. Sure, it'd have been a few more bytes per directory entry (to be specific, five more bytes!), but it was a lot more flexible -- and if more operating systems had been built with that "document types are metadata" idea, that metadata could have been replaced with MIME types later on, like it was on BeOS.