List of known Disk ][ protection schemes

[vladitx]

I don't know if this has already been done, but I need to gather information about used protection methods for upcoming imaging/emulation. Most of the information was provided by Toinet, but Deckard added as well. With every new piece of information I would be able to edit this post in an attempt to keep things sorted.

Known techniques

(0) Write-protection notch:
Simply requiring the diskette to be write protected.

(1) Prologue/epilogue change:
Substitution of standard RWTS address/data field prologues/epilogues (D5AA96/DEAAEB, D5AAAD/DEAAEB) with something else.

(2) Address field change:
Providing "incorrect" data in address field, e.g. wrong track number.

(3) Sector layout change:
Using non-standard sector size/count/layout, including different than 6+2 encoding.

(4) Nibble translation change:
Substitution of standard RWTS nibble table with something else.

(5) Nibble check:
Checking for certain nibbles, their timing in cycles (32, 36, 40, etc) and/or their count on a track. Nibble values may be used indirectly to decode further data.

(6) Non-standard tracks:
Placement of data on half/quarter tracks and/or track numbers higher than 34, in contrast to standard RWTS using only whole tracks (0 .. 34).

(7) Synchronized tracks:
Writing data on tracks in a special relation allowing to find certain data on different track(s) at precise moments in time (angular position).

(8) Partial tracks (spiralling):
Splitting data between tracks such as after reading part of one track and moving the head the stream will continue on some other track.

(9) Weak bits:
Leaving parts of medium weakly or un-magnetized such to allow formation of random transitions in the pulse shaper.

(10) Holes:
Damaging medium in specific positions such as certain sector's data, rendering runtime write attempts fail.

[vladitx]

I forgot to state that I welcome all corrections/additions.

There is a question: part #8, "Partial tracks (spiralling)". Does anybody know whether it continues to read stream during head movement or it stops during that period? On one hand, head movement (load) times will vary wildly between drives, but on the other the head is wide enough to compensate probably for the movement tolerance.

So, anyone with more precise description of this technique and/or example titles using it? This is my murkiest part so far ...

[Deckard]

[JPL]

You can see a track arcing here
http://www.hackzapple.com/DISKII/ARCING/ARCING.HTM

A DSL connexion is nice

[JPL]

A classification is here (in french sorry )
http://www.hackzapple.com/ORG1/MZ/PIRATESOFTS1.HTM

Never easy to do that but your system is nice too.

[JPL]

Weak bits : I never encountered this system on Apple II but only on IBM PC. Impossible to do a copy of course (as Prolok) but easy to remove.

[vladitx]

Thanks, guys. Would somebody be so kind as to translate the two paragraphs in English?

[Deckard]

[vladitx]

Deckard, are you sure this is the case for track Spiralling/Arcing? My question is only about it.

I can imagine that with the sufficiently wide head one can magnetize the stepper coils quarter-track inward/outward and still continue to be in "bounds" to receive the stream without interruption.

Toinet, do you happen to have dissected Skyfox code?

[JPL]

SPIRALING
That's not a real spiral form one side to and other in continum as the old music disks but a record of two, three ord four pages (ie sectors) on half track. (nota : you can do on quarter tracks of cause but on half track it's enough to have a disk very difficult to copy)

TRACK ARCING
Favorite form ECA , you wrote the same things as SPIRALING on 2 or 3 tracks but you come back : for this reason it's more hardly to copy

Suppose you cas see transform the circle of a track into a line

In DOS 33 you'll see the sectors XX as is :

Track X,0 __XX__XX__XX__XX__XX__XX__XX__XX __XX__XX__XX__XX__XX__XX__XX__XX
Track X,5 ________________________________________________________________
Track Y,0 __XX__XX__XX__XX__XX__XX__XX__XX __XX__XX__XX__XX__XX__XX__XX__XX
Track Y,5 ________________________________________________________________
(ok for explications I've draw as if synchronisation between the two tracks exist but in reality it's never do or if it's, that's an accident)


With SPIRALING You'll see

Track X,0 __XXXXXX________________________________________________________
Track X,5 _________________XXXXXX__________________________________________
Track Y,0 _____________________________XXXXXX______________________________
Track Y,5 ____________________________________________XXXXXX_______________

with TRACK ARCING you'll see
Or on

Track X,0 __XXXXXX__________________________________________________________
Track X,5 ___________XXXXXX_________________________________________XXXXXX_
Track Y,0 ______________________XXXXXX____________________XXXXXX___________
Track Y,5 _____________________________ ___________XXXXXX___________________

The resolution of the head is bad and can read sometime on half track but that's not a real reading, signals are nearest of strong noises than a good pulse

[JPL]

[vladitx]

EDIT: this one got somehow corrupted by ][ brackets

[vladitx]

Thanks for the nifty diagram, JPL. It's exactly what I supposed them to be. I called them "partial tracks" since they're basically the same, whether the head moving or not in a single direction only.

[JPL]

[toinet]