Fun!

I once made a Fat filesystem driver in JavaScript: https://www.quaxio.com/fat12js/index.htm

It's a FAT12 fs where a cycle has been hex edited into the file data to produce a 4GB repeating file on a tiny fs. Cute!

I had to read quite far before realizing it wasn't an over-explained article on sparse files.

One may wonder why the filesystem driver doesn't have cycle detection, but the fact that filesystem structures are generally considered trusted data, a cycle detection algorithm would add overhead and complexity, and the inherent (4GB) limit means that this is something better left to an application like chkdsk/fsck.

FAT is still the most widely used, lowest-common-denominator, non-proprietary filesystem so it's not going away anytime soon.