Christian Corti cc at
Tue Feb 2 02:55:33 CST 2021

On Mon, 1 Feb 2021, Al Kossow wrote:
> Imagedisk, even though it spends way too much time with the heads 
> spinning on the media at least does real-time retries. the problem is 
> you also need to be able to stop and assemble a complete image by 
> splicing together multiple partial attempts.

Well, isn't that logical? ;-)
I do this with my Linux implementation of IMD, and I do this with my 
floppy version of the mfmreader: immediately abort an operation when there 
are noises coming from the media, clean, restart at one/two cylinders 
before the forced abort, etc. and then "splice" together the individual 
read attempts.
You can't do real-time retries when reading at the flux level if you have 
no idea of the format. So often, it's better to sample a disk several 
times in case that the later processing reveals bad sectors. So often 
enough you can get an error free image produced from several samples.
The toughest part of course is the "PLL" that you need in software to lock 
to the bit rate.


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