Rotating memory data recovery

From: Tom Jennings <tomj_at_wps.com>
Date: Wed Sep 15 16:00:49 2004

On Mon, 2004-09-13 at 10:36, John Foust wrote:
> Anyone care to give a thumbnail sketch of what sampling rates
> would be necessary to digitize the signals on recording media
> (3 1/2", 5 1/4", 8" floppy, hard disks, drums, disk packs, etc.)
> at sufficient rates to preserve the encoding for post-processing
> in other tools?
>
> I saw one reference online that said 3 1/2" and 5 1/4" floppies
> were 250-500 kbit/s. If we were digitizing at a much higher
> rate than the original simple circuitry that might've only
> detected flux traversals, couldn't we recover more data?

I do not consider myself a magnetic-media expert, but I've made a number
of (low-density) controllers and en/de-coding schemes, and repaired
others, and read a lot (in one ear out the other probably).

I figure there are a few failure modes that would be easy for amateurs
(like me) to recover, like low-gain, dissipated magnetics (grain
randomization, etc), and such, that would be amenable to software
repair.

Data sleuthing like that being done on "Archimedes Method" palimpsest
(on TV last night, BTW) is way out of my league, but at least the raw
data would be there for future generations, etc.

Secondary issues might be, for example, the data on my LGP-21 platter is
fine, but the surface, now 40 years old, has changed physical structure,
however subtlely, and say, ruins heads/ruined by heads. So it's OK for a
day, week or month, then becomes bad. I think this is even likely.

It could be that, after bring-up, data snapshot and recovery, the
platter could be cleaned, re-polished, heads examined (including mine),
and simply put back into use.

I'm thinking that a light, in-place cleaning might be a good idea (using
70's tech cleaning aids for Eagle-type removable packs, down through the
head hole in the case) before spin up, but of course there's the danger
of doing harm.

It's all a gamble, and without a budget and even much time I'm not sure
how to approach it.
Received on Wed Sep 15 2004 - 16:00:49 BST