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Re: The Virtual Partition - say goodbye to FAT12

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"Rod Pemberton" wrote:
> "Mike Gonta" wrote:
>
>> deadlink://forum.osdev.org/viewtopic.php?f=1&t=30254

Hi Rod,

Sorry, dead link.

> I think James just misspoke ...  By "partition," I think
> he meant "filesystem image" which you call a "formatted
> image" in your osdev.org post.

No problem.

> So, you've taken a number of fields for a FAT32
> filesystem image which are normally not fixed and
> made them fixed fields, similar to a FAT12 filesystem
> image.

Actually, the "fixed" location analogy was in reference to
simplifying the the driver by using assumptions that for
practical purposes hold true. For example, on a 1.44 MB
floppy disk image (here I am safely assuming that the
physical floppy disk is long gone and forgotten even though
this is not really true - http://www.floppydisk.com/ )
just don't use the reserved sectors and the locations of
the fat tables and root directory can safely be assumed to
be fixed. While this keeps things simple, best practices
dictate that the locations should be calculated from the
BPB values. Doing so does not overly complicate the driver.
Concerning FAT32, just because something can be done,
doesn't mean that it ever will be done. For practical
purposes, the first root directory cluster will always be
cluster #2. The whole purpose of relocating it (as well as
having a backup copy of the boot sector - but not the
second stage - and a second - or more - copy of the fat
table are things of the past and completely redundant today
with flash media and modern hard drives anyways.

> This is so that you could modify a FAT12 driver to load a
> root directory and FAT tables from a FAT32 filesystem
> image, like what is normally done for FAT12. Is that the
> essence here?

Correct. Either modify an existing one or writing a new
one from the same simple specification (and thus avoiding
the unnecessary complications of a full blown driver in
favor of a simple one.

> At the end of your description, there is something about
> modifying certain values, e.g. "changed back to 17" and
> "keep track of the latest of these two values to go back
> and forth."  What is this about?

I had an idea that I could use the "Last Cluster Used"
field in the FAT32 FSI to "reserve" the Virtual Partition
clusters by changing the values back and forth depending
on which type of files were being written by which system.
At first it appeared that it would work, but the way that
Windows mounts a flash drive is complicated. The excellent
critique of "Robert Wessel" prompted me to do so more
extensive testing only to discover that I couldn't depend
on it to produce the desired results. As far as the the
who's doing what and when business goes - this will be
clearly explained (some might say as clear as mud) in the
AOD Virtual Partition Specification and Protocol which I am
still working on.

> Since this doesn't set up any actual partitions, it can
> only be used on devices that are recognized as removable
> media such as floppies and USB sticks, or filesystem
> images for emulators.

There are no such restrictions. The Virtual Partition will
work exactly the same (and perfectly fine) on a FAT32
partitioned volume.

>  I.e., this won't work on a device recognized as a hard
>  disk which needs to have a partition.

It will work perfectly fine in this (what I personally
believe to be a rather strange) situation as well.


Mike Gonta
look and see - many look but few see

http://mikegonta.com
http://tawk.to/mikegonta 

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Thread

The Virtual Partition - say goodbye to FAT12 "Mike Gonta" <mikegonta@gmail.com> - 2016-03-31 17:51 -0400
  Re: The Virtual Partition - say goodbye to FAT12 Robert Wessel <robertwessel2@yahoo.com> - 2016-03-31 20:48 -0500
    Re: The Virtual Partition - say goodbye to FAT12 "Mike Gonta" <mikegonta@gmail.com> - 2016-04-01 06:50 -0400
      Re: The Virtual Partition - say goodbye to FAT12 Robert Wessel <robertwessel2@yahoo.com> - 2016-04-01 11:06 -0500
        Re: The Virtual Partition - say goodbye to FAT12 "Mike Gonta" <mikegonta@gmail.com> - 2016-04-01 13:45 -0400
          Re: The Virtual Partition - say goodbye to FAT12 Robert Wessel <robertwessel2@yahoo.com> - 2016-04-01 17:06 -0500
            Re: The Virtual Partition - say goodbye to FAT12 James Harris <james.harris.1@gmail.com> - 2016-04-01 23:16 +0100
              Re: The Virtual Partition - say goodbye to FAT12 Robert Wessel <robertwessel2@yahoo.com> - 2016-04-01 17:29 -0500
                Re: The Virtual Partition - say goodbye to FAT12 Rod Pemberton <NoHaveNotOne@bcczxcfre.cmm> - 2016-04-01 20:24 -0400
                Re: The Virtual Partition - say goodbye to FAT12 Robert Wessel <robertwessel2@yahoo.com> - 2016-04-02 00:10 -0500
                Re: The Virtual Partition - say goodbye to FAT12 Rod Pemberton <NoHaveNotOne@bcczxcfre.cmm> - 2016-04-02 12:03 -0400
                Re: The Virtual Partition - say goodbye to FAT12 "Mike Gonta" <mikegonta@gmail.com> - 2016-04-02 20:19 -0400
                Re: The Virtual Partition - say goodbye to FAT12 "Mike Gonta" <mikegonta@gmail.com> - 2016-04-02 20:08 -0400
                Re: The Virtual Partition - say goodbye to FAT12 "Mike Gonta" <mikegonta@gmail.com> - 2016-04-02 20:02 -0400
                Re: The Virtual Partition - say goodbye to FAT12 "Mike Gonta" <mikegonta@gmail.com> - 2016-04-02 19:55 -0400
              Re: The Virtual Partition - say goodbye to FAT12 "Mike Gonta" <mikegonta@gmail.com> - 2016-04-02 19:30 -0400
            Re: The Virtual Partition - say goodbye to FAT12 "Mike Gonta" <mikegonta@gmail.com> - 2016-04-02 18:55 -0400
              Re: The Virtual Partition - say goodbye to FAT12 Robert Wessel <robertwessel2@yahoo.com> - 2016-04-04 00:40 -0500
  Re: The Virtual Partition - say goodbye to FAT12 "wolfgang kern" <nowhere@never.at> - 2016-04-01 09:20 +0200
    Re: The Virtual Partition - say goodbye to FAT12 "Mike Gonta" <mikegonta@gmail.com> - 2016-04-01 07:01 -0400
      Re: The Virtual Partition - say goodbye to FAT12 "wolfgang kern" <nowhere@never.at> - 2016-04-04 10:42 +0200
        Re: The Virtual Partition - say goodbye to FAT12 "Mike Gonta" <mikegonta@gmail.com> - 2016-04-05 15:58 -0400
          Re: The Virtual Partition - say goodbye to FAT12 "wolfgang kern" <nowhere@never.at> - 2016-04-05 22:19 +0200
            Re: The Virtual Partition - say goodbye to FAT12 "Mike Gonta" <mikegonta@gmail.com> - 2016-04-05 18:24 -0400
  Re: The Virtual Partition - say goodbye to FAT12 James Harris <james.harris.1@gmail.com> - 2016-04-01 09:55 +0100
    Re: The Virtual Partition - say goodbye to FAT12 "Mike Gonta" <mikegonta@gmail.com> - 2016-04-01 07:11 -0400
  Re: The Virtual Partition - say goodbye to FAT12 Rod Pemberton <NoHaveNotOne@bcczxcfre.cmm> - 2016-04-01 20:24 -0400
    Re: The Virtual Partition - say goodbye to FAT12 "Mike Gonta" <mikegonta@gmail.com> - 2016-04-02 21:30 -0400

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