Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!mips!ptimtc!nntp-server.caltech.edu!rknop
From: rknop@nntp-server.caltech.edu (Robert Andrew Knop)
Newsgroups: comp.sys.cbm
Subject: Re: Downloading GEOS files
Keywords: GEOS conversion
Message-ID: <1991Mar30.180559.13181@nntp-server.caltech.edu>
Date: 30 Mar 91 18:05:59 GMT
References: <20097@brahms.udel.edu> <1991Mar30.005550.3454@vlsi.polymtl.ca>
Organization: California Institute of Technology, Pasadena
Lines: 37

cinf07@vlsi.polymtl.ca (Miguel Pedro et Louis Sabbat) writes:
>Convert 3.1 (or 2.5 ?) is available at the Miton site. Actually, v2.5 is
>a newer version than v3.1 . It supports multi-file conversion.

Convert2.5 is indeed a newer version than 3.1, and is a lot nicer to use.  I
think the discrepancy in version numbers comes from the fact that several
people wrote upgrades of the original Convert in parallel.  2.5 uses a dialog
box to select files, whereas 3.1 stuffs them in a menu.  2.5 also knows if a
file is GEOS or not, so knows which way to convert it.  Finally, 2.5 can
convert to/from both PRG and SEQ files, whereas 3.1 can only do SEQ files (or
maybe that was 3.0, I can't remember).

2.5 is at milton in the (I believe) c64current directory.  Note that to avoid
a Catch-22, this file can unconvert itself.  Just load it and run it like a
normal non-GEOS c64 program, and it'll create a GEOS readable Convert on the
disk in drive 8.

>Someone on the net can probably give you more info on the structure of
>GEOS files. I don't have any book on GEOS, mostly because I don't use
>GeoProgrammer.

The diectory entry on a normal Commodore file has a pointer to the position on
the disk of the first block in the file; each block then points to the next
block, so only the one pointer is needed in the directory entry.  For GEOS
"sequential" files, this pointer serves the same purpose, but there is a
second pointer that points to the "header" block, which contains the picture
for the icon, and all the other stuff you can see by looking at the "INFO" on
a file.  For GEOS VLIR files, both pointers are also used; the header pointer
is the same as with sequential files, but the other pointe, instead of ponting
to the beginning of actual data for the file, points to an "index block,"
which is a collection of up to 127 pointers to strings of data blocks.

Note that both GEOS sequential and VLIR files are USR files in Commodore DOS.
GEOS sequential files should not be confused with SEQ files.

-Rob Knop
rknop@tybalt.caltech.edu