Yn.zip -

The file typically contained the 8080 assembly source code for a modem communication program.

In many digital document scans, "YN" followed by "ZIP" is simply a placeholder for "City, State, Zip " or a Yes/No field near a zip code entry. yn.zip

It was designed for CP/M , an operating system that preceded MS-DOS and was widely used on microcomputers in the late 70s and early 80s. The file typically contained the 8080 assembly source