3 Feb
2021
3 Feb
'21
10:34 a.m.
On Feb 3, 2021, at 1:27 PM, Al Kossow <aek at
bitsavers.org> wrote:
On 2/3/21 10:18 AM, Paul Koning wrote:
Which might mean either (a) what I suggested is in practice not needed, or (b) existing
software treats as unrecoverable disks that could be recovered with more sophisticated
tools. I have no idea which is correct.
Fair enough, but that means your real time
processing needs to be sufficient to know where the tracks are. And if the media are in
bad shape, you may in fact want to capture each track N times at slight offsets from the
nominal position, then do signal processing to recover the data as best you can.
That is in conflict with the requirement you spend as little time as you can on shedding
media
ideally, you'd use a 96tpi drive on 48tpi and microstep the head positioner. you
still have the
problem of head clog.
And, AFAIK, no existing software does any of this. Come to think of it, the techique of reading 1/2
inch tape with 36 track MR heads is somewhat similar: you get multiple readings of the
same nominal data track and can use the additional data to help with recovery.
In practice, the channels smear together, that's why John Bordynuik went to 36 tk
3490 heads from 18 tk 3480 heads on his 1/2" tape setups.
We saw this as well on the 6-track Whirlwind tapes using a 9-track head. Fortunately 6 of
the heads lined up cleanly.