Re: SpiraDisc Prolog Address

[mjmahon@aol.com (Michael J. Mahon)]

Bryan Parkoff wrote:

>    Is it true that all SpiraDisc always start at ProLog Address: D5 AA 96
>on track $0 and sector $0?  It is because $C600-C6FF PROM is programmed to
>start at ProLog Address: D5 AA 96.  After reading track $0 and sector $0,
>6502 assembly code instructs to read at a half or quarter track and/or read
>at a different ProLog Address such as D5 AA 97.

Yes, the boot sector (Tk 0, Sec 0) contains the code to continue reading
at least the next part of the boot code.  Since the Disk ][ boot ROM must
be able to read this sector, it is possible to manually trace the complete
boot process (though often tedious).

>    Is it how it works?  I understand that Copy II Plus has no way to
>duplicate SpiraDisc between source and destination unless we have to change
>the parameter.  Does it make sense?

It's more than a parameter.  It could be read "peicewise" by doing multiple
track reads at quarter-track spacings, but ot can only be written by doing
partial-track synchronized writes, so as not to overwrite the four adjacent
quarter (partial)track data.

>    How do privacy know to crack original disk by reading RAM.  All Apple
>II+ and later models have vector reset that prevents us from reading RAM
>when vector reset erases whole RAM.  We have to use original monitor without
>using AutoStart ROM that we can be able to read RAM without using vector
>reset.

Actually, all models prior to the //e do not seriously damage RAM
contents upon reset.

The desire to capture all of RAM unaltered (by, for example, the text
screen scrolling) is what led to the rise of IRQ cards like the WildCard.

>    Why do privacy prefer to create binary file from RAM while they give up
>reading SpiraDisc scheme?  Why can't they try to read SpiraDisc by using
>6502 assembly code instead of cracking software?

They could.  But the "assembly code" required is (potentially or actually)
different for each different protected title (sometimes version).  As a result,
it is not possible to create a "universal" program that can copy programs
with protection schemes designed after the copy program.  And having many
different strategies in anticipation of the future is always going to fall
short.
SpiraDisc is a protection strategy intended precisely to defeat the existing
track-oriented bit copiers.

_After_ SpiraDisc was developed, some copy programs could have added
analysis and copy routines precisely designed to defeat SpiraDisc.  Does
anyone know of any actual copy programs that did this?

>    It is my concern that some copy-protected games fail while playing.  For
>example, the players go to the high level from low level.  It will fail to
>load high level game.  I suspect that privacy takes unused sectors from
>track to track by putting privacy picture there.  The privacy picture might
>overwrite important data that high level is trying to read.  Does it make
>sense?

No.  Any such problem would be a bug in the game.

The real problem with copy-protected disks is that they become damaged
or wear out, rendering the program--which you paid to use--useless because
of media damage.

-michael

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