"Rubywand" <rubywand@swbell.net> wrote in message
news:3D5DE6E3.D3EB73B0@swbell.net...


>
>      Neat, Charlie! Thanks for the feedback.
>
>      The 64-byte 2MG prefix is the same for both disks. As an experiment, I
tacked
> on the prefix to an existing .dsk image of a game. It's in a .zip file on
GSWV at
> http://www.apple2.org.za/gswv/a2zine/Games/ . The file is
SuperQuestv551_2mg.zip .
> (There's also a Text file with game info: SuperQuestv551Directions.txt .)
>
>      If you decide to try the game, please post something about how it works
on
> XGS.
>
>
> Rubywand

Ok, first let me say that I'm not too familiar with XGS.  I have used it a few
times in the past but I believe that Kegs32r3 is so much better that I never
went back.  With that in mind I ran the SuperQuest 2mg image on Kegs32r3 first
to see how it was supposed to run.  It worked fine, which means that after
reading the introduction, naming and setting up my character, etc, and entering
the maze, I was killed in a matter of a few seconds.  This is normal for me in
games. <sigh>

I then tried the same in XGS.  It also worked but I did not know how to set the
speed in XGS to 1MHz so instead of lasting for a few seconds I lasted for a few
milliseconds.

One thing I should mention though.  If the point of the experiment was that you
could just add the 64-byte 2mg prefix to any .dsk image to make a .2mg image,
then be careful.

For one thing the two original 2mg images that you created with Asimov2 were
NOT exactly the same.  Byte $0C (zero based) of the 64 byte header is $00 for
TNILUTIL.2mg and $01 for PDUTIL.2mg.  $00 = DOS sector order, $01 = ProDOS
order.  There are also several offsets in the header that you have to pay
attention to.  One points to the start of the data which does not necessarily
have to start at the 65th byte.  Two other offsets point to optional
information that could be before or after the actually image data.  Of course
in the header you used the first offset did point to the 65th byte and the
other offsets were zeroes (not used) and you picked the DOS ordered header for
the DOS ordered .dsk image so everything worked.  Another possible problem is
that there are flags in the header for write protecting the image (needed for
some disks) and for DOS 3.3 volume number which is sometimes needed for the
disk to work.

Another quirk that I have noticed is that there are two versions of the 2mg
format, 0 and 1 (the version number is also in the header).  I am unsure of
what the differences are and if they have any affect on the normal operations
in XGS or Kegs32.

Charlie