In article ,
Elmo wrote:

I didn't realize these were the actual magnetic material. They are soooo
smooth and shiny. I expected concentric circular lines of something or
other like the bottom of a CDROM or DVD once it has been burned.

These platters are so polished that you can't make out a single bit of
"thin oxide" coating. Shinier than any metal or plastic mirror I've ever
seen and more indestructible than glass.

Older drives did use an oxide (like "ferric" magnetic tape cassettes).

Newer drives, such as the one which donated its platters for your
mirror, have a more complex magnetic recording layer. It's a complex
coating of alloys, vacuum-deposited on the polished aluminum (or glass
or ceramic) surface using a process known as sputtering. The
resulting magnetic layer has an extremely fine "grain" structure,
which allows for small magnetic domains and thus lots of storage per
area.

You won't be able to see the lines which make up the individual data
tracks... they aren't physically carved or burned into the magnetic
coating, and consist only of varying patterns of magnetism.

Yes, the surface is very smooth and shiny. It needs to be - the disk
drive heads "fly" over the surface, at a height far less than the
diameter of a human hair. Even a particle of cigarette smoke is too
big to fit between the "flying head" and the surface.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
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