| Megasoft shadow, by Jack Cornelius [message #189764] |
Tue, 19 February 2008 08:33  |
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Originally posted by: davemcmurtrie@gmail.com
I just picked up one of these boards, and I haven't been able to find
much information about it. I found one post in
comp.sys.amiga.emulators that claims this thing is supposed to be
inserted into a 1541 to allow copying of protected software, but it
never worked.
Can anyone provide any additional information about this thing? Is it
true that they didn't actually work? A user manual, perhaps?
Thanks,
Dave
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| Re: Megasoft shadow, by Jack Cornelius [message #189776 is a reply to message #189764] |
Tue, 19 February 2008 15:05  |
Wolfgang Moser
Messages: 632
Registered: July 2003
Karma: 0
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Senior Member |
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Hello Dave,
davemcmurtrie@gmail.com schrieb:
> I just picked up one of these boards, and I haven't been able to find
> much information about it. I found one post in
> comp.sys.amiga.emulators that claims this thing is supposed to be
> inserted into a 1541 to allow copying of protected software, but it
> never worked.
>
> Can anyone provide any additional information about this thing? Is it
> true that they didn't actually work? A user manual, perhaps?
at first many congratulations for this pickup, you surely
got some rare find and a true legend. Although, on the
other side, not of much real use when comparing one of its
advertisements with the actual software features -- as some
users tell.
Although I followed any discussion about The Shadow, the
selling company MegaSoft, one of its employees of that
time, Jim Drew or any of the later history with Utilities
Unlimited, the Supercard or Supercard Plus board and then
the Amiga stuff/crap(?)... There was no chance to pick up
any manual scans or something like that. Somone, I think
it was Raymond Day, sent me a scan from a magazine
advertisement and a photo from the board as plugged in
into a 1541 disk drive.
From some old stories, I believe it was "Jim Drew speaks"
from 1996, I know that wrote some sort of a new software
for The Shadow to replace the old nonfunctional one. That
software did make use of the drive RAM expansion only, but
did not use any of the other features of the board --
whatever these were.
Dave, as you are now a new owner of such a board, I really
would appreciate some nice high resolution photos from the
board. Upper side as well as back side. Better than just
making simple photos would be to actually scan the PCB with
a 600dpi scanner.
Some (more) informations as found in the net:
Google groups, most of these finds are related to that
hardware, but not all, have a look:
http://groups.google.de/groups/search?q=%22The+Shadow%22+-Ri sing+group%3Acomp.sys.cbm&start=0&scoring=d&lr=& amp;num=50&
Jim Drew interviews for background information:
http://c64preservation.com/jimdrew1.html
http://c64preservation.com/jimdrew2.html
Womo
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| Re: Megasoft shadow, by Jack Cornelius [message #189785 is a reply to message #189776] |
Tue, 19 February 2008 21:54 |
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Originally posted by: davemcmurtrie@gmail.com
On Feb 19, 3:05 pm, Wolfgang Moser <wn0...@d81.de.invalid> wrote:
> Dave, as you are now a new owner of such a board, I really
> would appreciate some nice high resolution photos from the
> board. Upper side as well as back side. Better than just
> making simple photos would be to actually scan the PCB with
> a 600dpi scanner.
>
Hi Womo,
Many thanks for the additional links you provided. My original
searches didn't turn up some of those conversations. I will provide
low-quality pics tomorrow taken with my phone, then higher quality (I
won't say high quality, because I'm not a great photographer) over the
weekend taken with a real camera. I'll follow up with a URL.
Thank you,
Dave
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| Re: Megasoft shadow, by Jack Cornelius [message #189797 is a reply to message #189787] |
Wed, 20 February 2008 07:43 |
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Originally posted by: davemcmurtrie@gmail.com
I put some horrible, low-quality images (taken from my phone) up at
http://www.andrew.cmu.edu/user/dave64/Commodore/shadow/
There's no html there -- just a directory index page. I'll put
something better up over the weekend when time permits, and when I
have a real camera available.
Thanks for all the information that folks have provided so far. I
never heard about these boards before I got this one, and it's
certainly an interesting story. It seems insane to me that Megasoft
would spend $400,000 on advertising for a product that they apparently
never tested.
Dave
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| Re: Megasoft shadow, by Jack Cornelius [message #189803 is a reply to message #189797] |
Wed, 20 February 2008 13:45 |
Wolfgang Moser
Messages: 632
Registered: July 2003
Karma: 0
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Senior Member |
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Awesome Dave,
davemcmurtrie@gmail.com schrieb:
> I put some horrible, low-quality images (taken from my phone) up at
> http://www.andrew.cmu.edu/user/dave64/Commodore/shadow/
that's the very first picture that I saw from a
backside of this The Shadow. It let's me know
that at least two ICs were intercepted with the
board and some longer high precision adapter
sockets. The 6502 as well as presumably the
floppy disk controller gate array.
> There's no html there -- just a directory index page. I'll put
> something better up over the weekend when time permits, and when I
> have a real camera available.
>
> Thanks for all the information that folks have provided so far. I
> never heard about these boards before I got this one, and it's
> certainly an interesting story. It seems insane to me that Megasoft
> would spend $400,000 on advertising for a product that they apparently
> never tested.
well .... ;-) That's how things screw up, when
you sold 'em before they got produced or even
engineered.
Womo
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| Re: Megasoft shadow, by Jack Cornelius [message #189808 is a reply to message #189797] |
Wed, 20 February 2008 15:10 |
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Originally posted by: bluebirdpod
On Feb 20, 5:43 am, "davemcmurt...@gmail.com"
<davemcmurt...@gmail.com> wrote:
> I put some horrible, low-quality images (taken from my phone) up athttp://www.andrew.cmu.edu/user/dave64/Commodore/shadow/
>
> There's no html there -- just a directory index page. I'll put
> something better up over the weekend when time permits, and when I
> have a real camera available.
>
> Thanks for all the information that folks have provided so far. I
> never heard about these boards before I got this one, and it's
> certainly an interesting story. It seems insane to me that Megasoft
> would spend $400,000 on advertising for a product that they apparently
> never tested.
>
> Dave
I remember that ad in a magazine back in the old day, but no one has
ever had the "gt package" with
the track and density display, I bought a 1541 with a external track
and density display from a guy in the groups over
10 years ago, he worked for Beckman multimeter makers. I bought it for
$25 back in the day, look at the post
http://groups.google.com/group/comp.sys.cbm/browse_frm/threa d/f9760bff5dde624a/ee345c2800a58508?lnk=st&q=wes+1541+tr ack+display+for+sale&rnum=1&hl=en#ee345c2800a58508
I have the plans on a geos file I think, maybe not geos, but its on a
1581 disk, Lemme dig it up and maybe I will find a place to post the
instructions, with a Supercard Plus board installed it would be a good
copier setup. the 1541 I bought has a real Supercard Plus board, but
it was the first release of it, and it plugs directly into the 6502
socket, later SCP boards had a 40 pin adapter and ribbon cable and the
board was placed on the side of the case outside of the sheilding.
strange though it does have the 1571 wire connection which is only
needed to map the ram so it can be used.
-BBP
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| Re: Megasoft shadow, by Jack Cornelius [message #190026 is a reply to message #190020] |
Sat, 23 February 2008 16:05 |
Wolfgang Moser
Messages: 632
Registered: July 2003
Karma: 0
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Senior Member |
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Hello Dave,
davemcmurtrie@gmail.com schrieb:
> As promised, I took better pictures and made them available:
>
> http://www.andrew.cmu.edu/user/dave64/Commodore/shadow/
oh wow that is amazing! I'm very happy about the bottom
side photography. It clearly tells about the authorship
from Mr. Cornelius -- be it a scam artist as Jim Drew
said sometime in 1992 or a genius otherwise.
On the top side I wonder what may be written to the left
side between the second and third little IC.
Too bad that nearly from all ICs the markings were
removed; quite a common technique for these days.
Professional-DOS (the fastest non-RAMdisk 1541 floppy
disk speeder of the world) author Klaus H. Roreger did
the same with his hardware -- with limited success since
I was able to decipher any IC type some years ago.
This may also be possible for The Shadow, if someone
really wants to invest some time (40 hours working time
I would estimate).
> Glenn, the advertisement thumbnail links directly to your site. If
> you'd like me to copy the image locally, or just remove it, please let
> me know.
Womo
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| Re: Megasoft shadow, by Jack Cornelius [message #190032 is a reply to message #190026] |
Sat, 23 February 2008 17:16 |
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Originally posted by: davemcmurtrie@gmail.com
On Feb 23, 4:05 pm, Wolfgang Moser <wn0...@d81.de.invalid> wrote:
> On the top side I wonder what may be written to the left
> side between the second and third little IC.
It says, "made in USA".
I told you I'm not a very good photographer ;)
> Too bad that nearly from all ICs the markings were
> removed; quite a common technique for these days.
On one of the two 40-pin ICs, you can still faintly read:
MOS
6502
3083
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| Re: Megasoft shadow, by Jack Cornelius [message #190053 is a reply to message #190032] |
Sun, 24 February 2008 02:56 |
Wolfgang Moser
Messages: 632
Registered: July 2003
Karma: 0
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Senior Member |
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Hi Dave,
>> On the top side I wonder what may be written to the left
>> side between the second and third little IC.
>
> It says, "made in USA".
> I told you I'm not a very good photographer ;)
aha, ok, I already got the impression that it must
be something simple like that. Thanks.
>> Too bad that nearly from all ICs the markings were
>> removed; quite a common technique for these days.
>
> On one of the two 40-pin ICs, you can still faintly read:
>
> MOS
> 6502
>
> 3083
Well, from Ramond Days old picture of his board:
http://d81.de/shared/1541-TheShadow.png
there is not only the 6502 CPU shown, but also the
floppy disk controller.
The third 40 pin chip may be identified by looking
onto its bottom side. Often people forget to
"protect" that side too by rubbing away all the
markings.
Womo
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| Re: Megasoft shadow, by Jack Cornelius [message #190076 is a reply to message #190053] |
Mon, 25 February 2008 10:52 |
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Originally posted by: bluebirdpod
On Feb 24, 12:56 am, Wolfgang Moser <wn0...@d81.de.invalid> wrote:
> Hi Dave,
>
>>> On the top side I wonder what may be written to the left
>>> side between the second and third little IC.
>
>> It says, "made in USA".
>> I told you I'm not a very good photographer ;)
>
> aha, ok, I already got the impression that it must
> be something simple like that. Thanks.
>
>>> Too bad that nearly from all ICs the markings were
>>> removed; quite a common technique for these days.
>
>> On one of the two 40-pin ICs, you can still faintly read:
>
>> MOS
>> 6502
>
>> 3083
>
> Well, from Ramond Days old picture of his board:
>
> http://d81.de/shared/1541-TheShadow.png
>
> there is not only the 6502 CPU shown, but also the
> floppy disk controller.
> The third 40 pin chip may be identified by looking
> onto its bottom side. Often people forget to
> "protect" that side too by rubbing away all the
> markings.
>
> Womo
Well after owning both SC and RB, I would have to say that Jim Drews
product has the potential to be more powerful, as said by Pete
Rittwage, the SC+ board will make IDENTICAL copies that are not
reframed such as Maverick does with the RB when making copies.,
However, the MNIB images need to be reframed for use with emulators,
funny. Guess GCR code is more elusive than we thought.
-BBP
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| Re: Megasoft shadow, by Jack Cornelius [message #190083 is a reply to message #190076] |
Mon, 25 February 2008 15:47 |
Wolfgang Moser
Messages: 632
Registered: July 2003
Karma: 0
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Senior Member |
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Hello bluebirdpod,
> Well after owning both SC and RB, I would have to say that Jim Drews
> product has the potential to be more powerful, as said by Pete
> Rittwage, the SC+ board will make IDENTICAL copies that are not
> reframed such as Maverick does with the RB when making copies.,
> However, the MNIB images need to be reframed for use with emulators,
> funny. Guess GCR code is more elusive than we thought.
it all depends on how precise you look onto the details.
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.
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.
Another protection technique that cannot be reproduced
from 1541 drive would be in-track bitrate changes that
were created of irregular bitrates that the 1541 cannot
create, but read. Let's say the 1541 is able to do 308,
286, 267 and 250 kBit/s on a nominal RPM of 300 1/min.
If you then record a track with 250 kBit/s and change
that to 258 kBit/s for only some 7 to 8 GCR Bytes inmid
a track, the 1541 will be able to follow the bit stream,
but it is definately not able to reproduce that. The
protection check can check the number of cycles that go
by for each GCR byte read and compare that with stored
values. Even if you adjust your drives RPM, you will
only be able to _either_ write with 258 or 250 kBit/s,
but you will not be able to do both and flip it inmid
a track write.
A could think of ways to fool the protection check, but
nevertheless you will be able to detect, if a disk is
an original or a copy, when you use an oscilloscope to
check that particular track for the bitrate change.
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.
Womo
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| Re: Megasoft shadow, by Jack Cornelius [message #190093 is a reply to message #190083] |
Mon, 25 February 2008 17:30 |
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Originally posted by: bluebirdpod
On Feb 25, 1:47 pm, Wolfgang Moser <wn0...@d81.de.invalid> wrote:
> Hello bluebirdpod,
>
>> Well after owning both SC and RB, I would have to say that Jim Drews
>> product has the potential to be more powerful, as said by Pete
>> Rittwage, the SC+ board will make IDENTICAL copies that are not
>> reframed such as Maverick does with the RB when making copies.,
>> However, the MNIB images need to be reframed for use with emulators,
>> funny. Guess GCR code is more elusive than we thought.
>
> it all depends on how precise you look onto the details.
>
> 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.
>
> 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.
>
> Another protection technique that cannot be reproduced
> from 1541 drive would be in-track bitrate changes that
> were created of irregular bitrates that the 1541 cannot
> create, but read. Let's say the 1541 is able to do 308,
> 286, 267 and 250 kBit/s on a nominal RPM of 300 1/min.
> If you then record a track with 250 kBit/s and change
> that to 258 kBit/s for only some 7 to 8 GCR Bytes inmid
> a track, the 1541 will be able to follow the bit stream,
> but it is definately not able to reproduce that. The
> protection check can check the number of cycles that go
> by for each GCR byte read and compare that with stored
> values. Even if you adjust your drives RPM, you will
> only be able to _either_ write with 258 or 250 kBit/s,
> but you will not be able to do both and flip it inmid
> a track write.
> A could think of ways to fool the protection check, but
> nevertheless you will be able to detect, if a disk is
> an original or a copy, when you use an oscilloscope to
> check that particular track for the bitrate change.
>
> 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.
>
> Womo
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.
What did the big software houses use, you said (Trace duplicator) ??
is that what most
publishers used, as I would think a normal 1541 not reliable to make
many tens of thousands
of duplicates. not to mention totally redundant having to open the
drive and change diskettes
constantly.
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| Re: Megasoft shadow, by Jack Cornelius [message #190288 is a reply to message #190088] |
Fri, 29 February 2008 05:47 |
Wolfgang Moser
Messages: 632
Registered: July 2003
Karma: 0
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Senior Member |
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Hi Christian,
christianlott1 schrieb:
> On Feb 25, 2:47 pm, Wolfgang Moser <wn0...@d81.de.invalid> wrote:
> how difficult would it be to make a h/w ipf reader/writer?
the hardware is available already, it is named
Catweasel. But it lacks software supporting IPF
dumping and remastering. Looking at recent
changes to german law I doubt that such software
will ever be written (in germany).
And then, even if you're able to make precise
_digital_ copies of a raw data stream you're
missing any analog effects that may help to
understand some copy protection any better.
Analog recording, dumping and/or storing
(samples) may also help to repair heavily
damaged images, so you always can go some
steps further in perfectionism.
As for now, preserving originals with MNib/
Nibtools is the method of choice for C64/1541
related titles. Now and then you need to
postprocess an image by hand to get a
remasterable image file, but that's it.
Womo
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| Re: Megasoft shadow, by Jack Cornelius [message #190289 is a reply to message #190093] |
Fri, 29 February 2008 06:00 |
Wolfgang Moser
Messages: 632
Registered: July 2003
Karma: 0
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Senior Member |
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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 did the big software houses use, you said (Trace duplicator) ??
> is that what most
> publishers used, as I would think a normal 1541 not reliable to make
> many tens of thousands
> of duplicates. not to mention totally redundant having to open the
> drive and change diskettes
> constantly.
I cannot present you any hard statistical facts,
but from reading many articles and WWW pages I know,
that of course sometimes plain 1541 disk drives were
used to copy disks.
Then there was the MSD dual disk drive, something
like a clone of the 1541, but special software was
available especially for disk duplication.
One type of a true professional duplication system
was the Tracer/ST machine series. It was built to
automatically duplicate a disk image onto a stack
of disks inserted.
This is a machine for 3.5" disks:
http://www.awp1.com/pctpro.html
I don't know what else was used to duplicate disks,
but there surely were more of such professional
systems. And all of these surely were able to dupe
C64 disks as well as Apple and Atari ones and disks
for MSDOS and UNIX systems.
Womo
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| Re: Megasoft shadow, by Jack Cornelius [message #190328 is a reply to message #190288] |
Sat, 01 March 2008 10:37 |
Groepaz
Messages: 640
Registered: December 2011
Karma: 0
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Senior Member |
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Wolfgang Moser wrote:
> Hi Christian,
>
> christianlott1 schrieb:
>> On Feb 25, 2:47 pm, Wolfgang Moser <wn0...@d81.de.invalid> wrote:
>> how difficult would it be to make a h/w ipf reader/writer?
>
> the hardware is available already, it is named
> Catweasel. But it lacks software supporting IPF
> dumping and remastering. Looking at recent
> changes to german law I doubt that such software
> will ever be written (in germany).
its on my list. there is actually an exception in the dcma (and also
european law) which allows it to dump <whatever> from "obsolete" media to
modern media for backup purposes *even* when circumenventing copy
protection.
but for now, i am slowly fixing the various bugs you reported (thanks for
that btw =))
that said, raw dumping doesnt have high priority right now, because the vast
majority wants to transfer "cooked" images (not even gcr images, which are
on my list too ofcourse). i'll add some features to help reading "bad"
disks first, and improve handling 40 track stuff.
--
http://www.hitmen-console.org
http://www.pokefinder.org
http://ftp.pokefinder.org
It is dangerous to be right when the government is wrong.
<Voltaire>
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| Dumping protected disks with Catweasel, Was: Megasoft shadow, by Jack Cornelius [message #190351 is a reply to message #190328] |
Sun, 02 March 2008 08:16 |
Wolfgang Moser
Messages: 632
Registered: July 2003
Karma: 0
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Senior Member |
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Hi Groepaz, wou wrote::
> Wolfgang Moser wrote:
>> Hi Christian,
>>
>> christianlott1 schrieb:
>>> On Feb 25, 2:47 pm, Wolfgang Moser <wn0...@d81.de.invalid> wrote:
>>> how difficult would it be to make a h/w ipf reader/writer?
>> the hardware is available already, it is named
>> Catweasel. But it lacks software supporting IPF
>> dumping and remastering. Looking at recent
>> changes to german law I doubt that such software
>> will ever be written (in germany).
>
> its on my list. there is actually an exception in the dcma (and also
> european law) which allows it to dump <whatever> from "obsolete" media to
> modern media for backup purposes *even* when circumenventing copy
> protection.
Don't know, if it is applicable here. Who defines
what is called 'obsolete'? Currently enough "player
devices" are available in working condition (C64
with 1541).
> but for now, i am slowly fixing the various bugs you reported (thanks for
> that btw =))
Oh, it got through to you? A short note about the
receipt would have been fine.
> that said, raw dumping doesnt have high priority right now, because the vast
> majority wants to transfer "cooked" images (not even gcr images, which are
> on my list too ofcourse). i'll add some features to help reading "bad"
> disks first, and improve handling 40 track stuff.
Well, maybe it would be possible to make ARJuna
work again with the current Catweasel driver. I
know that Christoph had to extend the driver a bit
so that the raw data stream was accessible from
userspace. To me it seams that this driver
extension does not work for ARJuna currently.
Although ARJuna is not _that_ userfriendly, it
would be an alternative to produce G64 files. Let's
hope I remember how to configure the 'playfield' ;-)
Womo
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| Re: Megasoft shadow, by Jack Cornelius [message #386433 is a reply to message #190083] |
Tue, 27 August 2019 13:55 |
sales
Messages: 12
Registered: April 2008
Karma: 0
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Junior Member |
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> 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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| Re: Megasoft shadow, by Jack Cornelius [message #386434 is a reply to message #190289] |
Tue, 27 August 2019 13:59 |
sales
Messages: 12
Registered: April 2008
Karma: 0
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Junior Member |
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> 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?
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