Re: disk image emulator on the GS - possible?

["John B. Matthews" <nospam@nospam.invalid>]

In article 
<7fe3adf4-8381-4a29-8d83-c622fd97e059@h18g2000yqj.googlegroups.com>,
 schmidtd <schmidtd@my-deja.com> wrote:

> 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.

Egad! I completely forgot:

<http://applecommander.cvs.sourceforge.net/viewvc/applecommander/AppleCom
mander/src/com/webcodepro/applecommander/storage/Disk.java?revision=1.26&
view=markup>

-- 
John B. Matthews
trashgod at gmail dot com
<http://sites.google.com/site/drjohnbmatthews>