10 ms·

Maybe magnetism could work. HDD platters take very strong fields to change magnetization these days, so erasing the data with the positioning magnet(s) seems av

Maybe magnetism could work. HDD platters take very strong fields to change magnetization these days, so erasing the data with the positioning magnet(s) seems avoidable.

amelius 2y ago
So write too many zeros to your drive, the disk becomes demagnetized, and the head will crash?
- Faaak 2y ago
  With another encoding like Manchester, it wouldn't;-)
- frud 2y ago
  The raw words written to the drive are actually re-encoded into slightly larger codewords with nice properties like not having too many zero or one bits in a row, and error detection/correction. Plus I think that the 0/1 bits are not encoded as "no magnetism"/"some magnetism", but instead as "north magnetism"/"south magnetism" since magnetic fields have a direction. And I don't think the magnetic fields on the platters have any appreciable effect on the head besides the electromagnetic effects at the sensor.
- Cerium 2y ago
  Essentially the same problem as with fiber optics. The data can't be recovered unless there are frequent bit transitions. In that case the data is transformed to ensure illegal patterns cannot occur.
perihelions 2y ago
Also, you could imagine a magnetic bearing whose field strength rapidly diminishes as you move away from it, due to cancellation, like a Halbach array [0]. I wonder if there's a simple geometric configuration for a bearing that has this property, as well as the critical property of passively stable levitation, maybe based on diamagnetic or superconducting materials [1]. edit: Maybe something in this direction? [2] [0] https://en.wikipedia.org/wiki/Halbach_array https://en.wikipedia.org/wiki/Halbach_array [1] https://en.wikipedia.org/wiki/Magnetic_bearing https://en.wikipedia.org/wiki/Magnetic_bearing [2] https://ntrs.nasa.gov/api/citations/20070006849/downloads/20070006849.pdf https://ntrs.nasa.gov/api/citations/20070006849/downloads/20... ("Development and Testing of a Radial Halbach Magnetic Bearing")

Maybe magnetism could work. HDD platters take very strong fields to change magnetization these days, so erasing the data with the positioning magnet(s) seems avoidable.

amelius 2y ago

So write too many zeros to your drive, the disk becomes demagnetized, and the head will crash?

Faaak 2y ago
With another encoding like Manchester, it wouldn't;-)
frud 2y ago
The raw words written to the drive are actually re-encoded into slightly larger codewords with nice properties like not having too many zero or one bits in a row, and error detection/correction. Plus I think that the 0/1 bits are not encoded as "no magnetism"/"some magnetism", but instead as "north magnetism"/"south magnetism" since magnetic fields have a direction. And I don't think the magnetic fields on the platters have any appreciable effect on the head besides the electromagnetic effects at the sensor.
Cerium 2y ago
Essentially the same problem as with fiber optics. The data can't be recovered unless there are frequent bit transitions. In that case the data is transformed to ensure illegal patterns cannot occur.

perihelions 2y ago

Also, you could imagine a magnetic bearing whose field strength rapidly diminishes as you move away from it, due to cancellation, like a Halbach array [0]. I wonder if there's a simple geometric configuration for a bearing that has this property, as well as the critical property of passively stable levitation, maybe based on diamagnetic or superconducting materials [1]. edit: Maybe something in this direction? [2] [0] https://en.wikipedia.org/wiki/Halbach_array https://en.wikipedia.org/wiki/Halbach_array [1] https://en.wikipedia.org/wiki/Magnetic_bearing https://en.wikipedia.org/wiki/Magnetic_bearing [2] https://ntrs.nasa.gov/api/citations/20070006849/downloads/20070006849.pdf https://ntrs.nasa.gov/api/citations/20070006849/downloads/20... ("Development and Testing of a Radial Halbach Magnetic Bearing")