On Tue, 04 May 1999 09:08:09 -0400 "Michael S. Lorrey" <firstname.lastname@example.org> writes:
Some iron oxides are
>ferromagnetic, others are not. I'm not sure the proper molecule for
>the ferromagentic types, but once extra oxygen gets added on, its
>toast. The precious metals apparently are alloyed or compounded with
>the ferrous oxide and aids stability. I'll check on this, but I do
>know that while standard old tapes will usually develop bad blocks
>near the beginning of the tapes (closest to the outside environment),
>the gold, platinum, and silver tapes tend to remain error free unless
>they've been misused. They also read and write much faster (fewer
>rewrites) than standard tapes. The other day I used a silver tape
>dated 1963 and it read and wrote cleanly.
Thanks for the elaboration. Whereas most audio tapes, the kind I was thinking of, are so-called 'normal bias' or 'Type I' tapes, and use an iron compound, there are also so-called 'high bias' or 'Type II' audio tapes which use chromium dioxide, and they are sometimes called 'metal tapes'. I checked one reference book which indicated that floppy diskettes are coated with ferrite, and that modern hard disks are aluminum, covered with a thin (0.05 to 0.2 micron) layer of cobalt, which holds the data, topped by a thin layer of graphite.