Re: disk image emulator on the GS - possible?

[schmidtd <schmidtd@my-deja.com>]

On Jul 2, 9:52 pm, "John B. Matthews" <nos...@nospam.invalid> wrote:
> In article <fHc3m.511$P5....@nwrddc02.gnilink.net>,
>
>
>
>  "Charlie" <charlieD...@verEYEzon.net> wrote:
> > "John B. Matthews" <nos...@nospam.invalid> wrote in message
> >nospam-39CE32.17130802072009@news.aioe.org">news:nospam-39CE32.17130802072009@news.aioe.org...
> > > In article <1OydnUMe6ZzUY9HXnZ2dnUVZ_gidn...@giganews.com>,
> > > "Michael J. Mahon" <mjma...@aol.com> wrote:
>
> > >> Charlie wrote:
>
> > >> > Also the 2mg format allows for comments anywhere in the image.  
> > >> > Although I've never seen an image that used this feature, it
> > >> > wouldn't surprise me to find one.
>
> > >> That sounds like a *terrible* idea.
>
> > >> A disk image is a regular structure that can be indexed into.
> > >> Interpolating "comments" demands sequential reading for a
> > >> negligible value.
>
> > >> This "feature" should be removed from the .2mg "standard".
>
> > >> If the comments are part of the header, they would make it a
> > >> variable-length header, which is also a big downside for a
> > >> small upside.
>
> > >> The only "minimally-distruptive" way to add comments to an
> > >> image would be to suffix them--and even that makes the size
> > >> of an image vary, which most would interpret as an error.
>
> > > Quite right. It looks like the (optional) comment is found after the
> > > disk image data itself.
>
> > > <http://apple2.org.za/gswv/a2zine/Docs/DiskImage_2MG_Info.txt>
>
> > Yes, that is version 1 of the 2mg format (documented by Eric Shepherd in
> > 1999 I believe).  It is the better of the two I've seen since it spells
> > out where the comments and creator data should go.  Unfortunately, there
> > is an earlier version 0 (I believe  documented by Thomas Fok who wrote
> > Revival) of the format that does not define where the comments and
> > creator data should go (I don't have a working link to that version any
> > more).  When writing a program to use a 2mg image you could look at the
> > version number to determine whether you need to delve further into the
> > structure of the file.   Or you could just assume that nobody has ever
> > put a comment in a stupid place.  My luck, 5 minutes after I put such a
> > program on the internet I'd get an email from somebody complaining about
> > how my program couldn't read their 2mg files :-)
>
> Interesting. I recall a 2mg image passing by recently; it appeared to be
> v1 in having a suffix comment. Andy McFadden puzzled it out for
> CiderPress, but I've misplaced the thread.

AppleCommander handled them incorrectly at first too; I got to repair
that one as well.