Hard disks use a run-length limited encoding, so the number of magnetic 1s and 0s remains roughly constant no matter what logical 1s and 0s you store.

https://en.wikipedia.org/wiki/Run-length_limited

Oh wow. And now that I read this, it dawned on me that any memory technology that is based on storing charge (like DRAM) will have actual, albeit also very very theoretical, mass differences depending on bit value as well...

The internet weighs about 50 grams: https://youtu.be/WaUzu-iksi8