• Re: Megasoft shadow, by Jack Cornelius

    From sales@cbmstuff.com@3:770/3 to All on Tuesday, August 27, 2019 10:59:17
    Hi bluebirdpod,
    Hey Womo, did you ever figure out, what speed dos, JD stole to use in
    the SC+ rom ??
    most likely he patched a speed dos to use.

    no, I did not find any bigger similarities between
    SpeedDOS and the SC+ ROM. For JiffyDOS I cannot tell
    since I didn't investigate that in depth.

    There are of course greater similarities between
    some routines from the Professional-DOS speeder
    system (RapidDOS Pro in the US, DemonDOS in the UK)
    and SC+, some routines that make absolutely no sense
    for SC+ since it misses the GCR decoding tables as
    well as the nybble shifting hardware.

    Maybe this was bad coincidence or just made to
    obfuscate any code reverse engineers, I don't know.

    What are you referring to here?

    --- SoupGate-Win32 v1.05
    * Origin: Agency HUB, Dunedin - New Zealand | Fido<>Usenet Gateway (3:770/3)
  • From sales@cbmstuff.com@3:770/3 to All on Tuesday, August 27, 2019 10:55:25
    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
    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.

    --- SoupGate-Win32 v1.05
    * Origin: Agency HUB, Dunedin - New Zealand | Fido<>Usenet Gateway (3:770/3)