Re: WildCard By Central Point Question

[Dennis Doms <SynABit@everest.invalid>]

Andy McFadden wrote:

> Bryan Parkoff <BParkoff@satx.rr.com> wrote:
>>     I understand that it is SpiraDisc.  How does SpiraDisc block
>>     Apple II
>> users from reading data using nibble editor.  Is it true that we have
>> to read 6502 code (assembler) from the track 0 sector 0 before we can
>> understand what 6502 code (assembler) manipulate with the disk?
> 
> It uses quarter-tracking.  Apple II 5.25" disk drive controllers give
> software direct control over the stepper motor, so you can do funky
> things
> like freeze the head partway between tracks.  This didn't work on some
> 3rd-party 5.25" drives, causing certain people to lend certain other
> people copies of Frogger, which subsequently got cracked, written up,
> and submitted to COMPUTIST.
> 
> (Try that today and the DMCA police would have you in jail.)
> 
> Anyway.  You need to get the data from the tracks *and* have it
> properly synchronized, so that when they move from track 0 to track
> 0.25
> the next set of data is right under the read head.  If the data
> doesn't show up quickly enough, they know it's a copy and the boot
> fails.

I don't know that I ever saw a disk that formerly "quarter-tracked". 
What I saw were disks that wrote a segment of a track, stepped a half 
track, wrote another segment of a track, etc., so that the segments 
never overlapped on adjacent tracks. The controlling software could 
time out whem to "step", but a copy program might was usually unable to 
duplicate this since most of them worked solely on half-track steps and 
with the assumption that no tracks were laid closer than one track 
apart (that is, you might find a track at 3.0 and 4.5 and 5.5, but not 
3.0 and 4.0 and 4.5).

> Copying is tricky because there's a lot of "leakage" from adjacent
> half-tracks.  If you tried to write the disc as a series of tracks,
> you'd be stepping on the half-tracks and quarter-tracks to either
> side. Which might work out okay if you could get the synchronization
> just right.

I was told (by people I presumed knew more than me :) that the stepper 
motor design of Apple 5.25 drives only positioned reliably to 
half-track positions. (Bit) Copy programs _did_ implement an effort to 
position the head at quarter-track increments in order to attempt to 
copy spiralled disks; the idea was that if you copied the spiralled 
tracks at the quarter-track position between the half-track spiral that 
you would get 3/4 of each segment. That hopefully would provide enough 
signal for the disk head to "bite" on. The head was positioned by 
starting a half-track positioning move and then "aborting" in such a 
way that the head only moved part of the distance, but the people I 
talked to said the positioning was not precise on typical drives. 
Therefore you might need to retry on any tracks where the boot 
"stalled" to see if you lucked into better positioning.

You could check the success of tracks on the original Disk II drives by 
removing the cover and marking the head positioning cam in track 
increments. You booted the attempted replicant disk and watched for the 
head movement to "hang"; that was usually an indication the read at 
that position had failed (some peograms would reboot on failure to make 
it more difficult to see).

> Spiradisc was a thing of beauty.  I wish I could find my write-up of
> the Maze Craze disk, which had a disk-present check that Frogger
> didn't. I also truncated the Frogger write-up severely because I just
> referred to the Maze Craze discussion (i.e. there's not a lot of
> details about
> the protection itself).  Sadly, the Maze Craze "softkey" was rejected
> for publication, so if I can't find it then it probably doesn't exist.

The first one I saw was Lifesaver (a very useful disk recovery utility; 
can't recall the software company at the moment). The boot process was 
almost an artistic experience, and _fast_; a single-load disk where the 
head appeared to make two continuous swipes (actually half-track steps, 
but so rapid as to seem smooth) across the disk and the program was up. 
Just the distinctive sound of the head sweep was sometimes a giveaway.

-- 
Dennis Doms SynABit@Everest.invalid
[ObSpamFoil: replace ".invalid" with "kc.net" to send real mail.]
"We aren't here to rule. We aren't here to bring chaos or anarchy.
 We're here to end the reign of criminals." - Batman, _The Dark Knight_


-----------== Posted via Newsfeed.Com - Uncensored Usenet News ==----------
   http://www.newsfeed.com       The #1 Newsgroup Service in the World!
-----= Over 100,000 Newsgroups - Unlimited Fast Downloads - 19 Servers =-----