paulkoning at comcast.net
Wed Feb 3 12:34:57 CST 2021
> 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:
>> 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.
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.
>> 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.
Yes, I was thinking of that issue while looking into how a 10 track tape would look to, say, a 16 track instrumentation recorder head. The picture looked marginal at best.
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