The 'femtotech from HDD' thing is essentially shorthand for some kind of black swan. Considering how powerful mere human-level intelligence is, superintelligence seems certain to find something overpowered somewhere, even if it's just hacking human minds.

FWIW, while my estimate of femtotech-through-weird-bit-patterns is effectively zero, my estimate of femtotech through rewriting the disk firmware and getting it to construct magnetic fields in no way corresponding to normal disk usage is.. well, still near-zero, but several orders of magnitude higher.

If you didn't consider overwriting the firmware as an immediately obvious option, you may be merely human. An AI certainly would, and other options I wouldn't think of. :-)