Toinet wrote:
> On 23 jan, 23:45, "Michael J. Mahon"  wrote:
>> Andy McFadden wrote:
>>> In comp.sys.apple2 e...{at}neilsonhart.com wrote:
>>>> I believe a straight Nibble copy will get you pristine backups of
>>>> Ultima I-IV.
>>> IIRC, Ultima I just used altered address / data fields, but Ultima II
>>> added some sort of secondary check (nibble count?) which .nib
won't handle.
> 
> Ultima I alters the address and data fields.
> Ultima II adds a nibble count.
> Ultima III alters the address and data fields and uses false opcodes.
> Ultima IV adds a nibble check and alters the address fields depending
> on the filename (see. http://www.hackzapple.com/phpBB2/viewtopic.php?t=46)
> Ultima V adds 16 to the sector number ;-)
> 
>>>> As far as I know, no other emulator supports the .v2d
format which is
>>>> a shame because it's an open standard.
>>> Where is this open standard published?  Google didn't turn up much, but
>>> perhaps I was searching for the wrong things.  I'm curious to see how
>>> different sync-byte widths are represented.  (I'd also like to see an
>>> uncracked "spiradisc" Frogger image boot.)
>> Right!
>>
>> Adding support for quarter-track disks will only incrementally
>> increase the number of protected disks that can be represented.
>> Many protections lie outside the realm of quarter-tracked .nib
>> representation, even if the tracks are "synced".
>>
>> It would be very helpful if a "census" of disks and the
protections
>> they rely on were available, so that the cost/benefit ratio for
>> incremental additions of capability could be quantitatively assessed.
>>
>> -michael
>> (cut cut)
> 
> Nearly 100% of Electronic Arts programs use a sort of spiralling on
> three tracks at the beginning of a disk: the track-arcing.
> Sirius programs were put on half tracks only.
> Hold-Up by Infogrames uses spiralling on the whole disk, a curiosity.

I'd think that once you've written a spiraling RWTS, it would actually
be easier to use it for everything but track 0.  ;-)

> The number of programs that use .25 tracks is close to 0 compared to
> the quantity of Apple II programs.

I'm sure that's correct, since spira-disk and other sophisticated
copy-protection schemes were relatively "late in the game" and
expensive to apply.  As a result, more sophisticated mechanisms
tended to be used with titles that were expected to be in demand
by more users.

So it may be necessary to estimate the "value" of the protected
program and use that to weight the value of being able to run it.

Of course, the "value" of running a particular program today may
be quite different from its perceived value when it was published.

In any case, if a format were developed that was only, say, twice
the size of a typical .dsk or .nib image, but that supported, say,
99% of the desirable programs, that would be a fine tradeoff.

On the other hand, a format requiring 4x the space to pick up
just 90% of the protected titles would be less interesting, and
less likely to inspire wide emulator and tool support.

For reasons discussed at length in the past, there will always
be protected disks that, even though they can be imaged in some
yet-to-be-defined format, could not be re-written to a real disk
by a Disk ][ without doing the manual normalization work on an
emulator.

-michael

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