Ultimate FDC? (Was: IBM 6360 - Filesystem(ish) info?

Fred Cisin cisin at xenosoft.com
Tue Feb 19 19:31:46 CST 2019

On Tue, 19 Feb 2019, Paul Koning wrote:
> I' reminded of the Bordynuik tape reading machine that uses an MR head. 
> Capturing analog flux levels at, say, 10x the nominal flux change 
> density means all the rest is simply digital signal processing.  That 
> can be done in real time if you must, but much more easily in post 
> processing using whatever tools and languages you like.

As Al pointed out, at least an initial stage of analysis should be done 
real-time, or close to that, to determine whether the read seemed to have 
been successful.  'Course, that doesn't preclude later stages from 
also requesting a new attempt, if the data doesn't look good on further 

And, of course,  using multiple machines, or just multiple processes, one 
system could begin processing, while another is reading more tracks.
The reliability encountered would determine how much testing should be 
done before moving on, either to the next track?  or the next disk?
If errors are RARE, then there would be no cause to hesitate and hand off 
processing while moving on to the next JOB.
If errors are FREQUENT (Al, Chuck, and I dealt with some that required 
dozens of attempts to get a successful read of a track), then that would 
caall for MORE processing before stepping to the next track or disk.

FDC does a CRC "real time", and compares that with the value stored in the 
sector header.

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