On Mon, Dec 11, 2017 at 09:16:35AM -0500, rhkramer@gmail.com wrote:
On Monday, December 11, 2017 01:12:41 AM Gene Heskett wrote: > There are instructions for making the pi's boot from rust, but its a one > way as its said to be an otp rom in charge of that, however when I try > to set that bit, its write protected even for root. In all 3 of the pi's > I bought. And there is even less info around on how the rock64 boots. I know "rust" is used as sort of a slang term, but do hard disks have iron oxide anywhere on them? When I take a hard disk apart (I save the magnets and melt the media), the disks are nice and shiny. (Did hard disks ever use iron oxide?) I guess I can google, and will try that later today. Oh, well: From the Wikipedia article on "Magnetic storage": https://en.wikipedia.org/wiki/Magnetic_storage#Design "For reliable storage of data, the recording material needs to resist self-demagnetisation, which occurs when the magnetic domains repel each other. Magnetic domains written too densely together to a weakly magnetisable material will degrade over time due to rotation of the [1]magnetic moment one or more domains to cancel out these forces. The domains rotate sideways to a halfway position that weakens the readability of the domain and relieves the magnetic stresses. Older hard disk drives used [2]iron(III) oxide as the magnetic material, but current disks use a [3]cobalt-based alloy.[4][1]" I have trouble understanding that 2nd sentence: "Magnetic domains written too densely together to a weakly magnetisable material will degrade over time due to rotation of the [5]magnetic moment one or more domains to cancel out these forces." and would like to rewrite it to be more clear--I'll make an attempt below--suggestions are welcome: "Magnetic domains written too densely together to a weakly magnetisable material will degrade over time--the magnetic forces which impact the disk during rotation will cause one or more of the tiny magnetic domains to rotate to (partialy) cancel out the intended magnetization (which stores the data)."
Be careful. As I understand it, the force which causes the demagnetisation has little, if anything, to do with rotation of the platter. Rather, the problem lies in the fact that, let's say you have 1-0-1 stored on the disk, those two 1s provide a force which "pulls" on the 0 until it looks more like a 1 than a 0.
I'll probably also replace "too densely together" with either "too close together" or "too densely". Maybe I've combined too much of the third sentence into the second sentence and it might stand rewriting as well. References Visible links 1. https://en.wikipedia.org/wiki/Magnetic_moment 2. https://en.wikipedia.org/wiki/Iron%28III%29_oxide 3. https://en.wikipedia.org/wiki/Cobalt 4. https://en.wikipedia.org/wiki/Magnetic_storage#cite_note-AutoMK-13-1 5. https://en.wikipedia.org/wiki/Magnetic_moment
-- For more information, please reread.
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