Subj : Re: Megasoft shadow, by Jack Cornelius
To   : All
From : sales@cbmstuff.com
Date : Tue Aug 27 2019 10:55 am

> Even SC+ is not able to make an identical copy of a
> certain disk. As Jim Drew explained somewhere, the true
> halftrack protection from Bounty Bob Strikes Back!
> cannot be reproduced with the native copier for the SC+.
> Instead Jim wrote a custom copier after he analyzed the
> protection.
> By analyzing a protection and then creating a mastering
> routine that will recreate that protection does mean
> that this is not a _copy_, but a re-master.

That is not the case.  The Bounty Bob Strikes Back! Copier is an actual copier. 
 It is just a custom copier that knows which tracks are 1/2 tracks and which 
are not.  Since the main copiers for Supercard+ do not support 1/2 tracks, a 
custom copier was 
needed.  Copying Bounty Bob Strikes Back! is a two part process - first you 
copy the disk with the GCR Nibbler and then you copy it again using the custom 
copier.

 
> And further true copier machines (Trace duplicator) are
> able to create patterns that can be detected with a 1541
> disk drive, but cannot be written with 'em, even if you
> do adjust the motor speed. E.g. true Fat Tracks that are
> recorded over two adjacent halftracks. If you try to
> replicate that, then you would always overwrite one of
> the both halftracks due to mechanical issues. The 1541's
> R/W head is a so named tunnel erasing head. It write a
> wider track and after that the left and right side of
> that wide track are erased again after. This sharpens
> the track and it can be better reread after. In fact I
> never saw such a true Fat Track protection, mostly these
> were only precisely aligned adjacent full-tracks.

If you disable the erase head you can write a 1/2 track.  However, you need to 
first erase the disk with a magnet.  EA used true 1/2 track protection, with 
tracks 34, 34.5, and 35 all containing valid sectors for the entire track.

 
> Reframing btw. is no magic issue. And because Jim Drew
> does not explicitly tell about all the nifty tricks that
> he used to make the copiers work does not mean that he
> did not use something similar to reframing for SC+.
> Since no 1541 drive runs at the very same RPM as the
> drive the original disk was recorded for, you always
> have to do SYNC and GAP length reducing/increasing,
> maybe RPM adjustments and some sort of reframing or
> frame detection (perhaps tail GAP detection too) on
> SYNC-less tracks.

I never changed gap lengths or anything else GCR related, and I didn't re-frame 
any data.  The only real change was a reduction of the drive speed to 298.1 
RPMs.

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