That reminds me of a blog post where the author managed to run Linux on an HDD, that is, not only using the HDD as the storage media for a Linux install, but instead running the kernel on the HDD's internal IO controller, SOC inside the HDD that actually runs the plates and everything.
Unfortunately I could never find that post again, because all searches for running Linux on HDD return obvious results for using the HDD as an install media, not as the computer.