So the next step is file system. Well we already know FAT, like Microsoft, we
can bitmap the CVF allocation table, 0 meaning unused and 1 meaning used. The
largest capacity of the BitFAT (assuming a 512MB CVF) is 128K( following MS
standard).
Now according to the MS-DOS programmers reference, the MDFAT (or DoubleSpace
File Allocation Table) consists of a series of 4 byte entries. They map FAT
clusters to sectors in the sector heap. There is one entry for each cluster on
the compressed drive. The entries specify the location of the sectors in the
heap that contain the data for the cluster and flags to indicate status (i.e.,
in use, compressed, and the size of the cluster). MDFAT is a function of the
max capacity of the CVF, The largest capacity is 512MB for a CVF so the largest
MDFAT size is 256K
So, 384K in accounting using the Microsoft method, assuming direct
implementation.
> From: [EMAIL PROTECTED]
> To: [email protected]
> Date: Fri, 28 Mar 2008 12:13:48 +0000
> Subject: Re: [Freedos-devel] compressed FAT filesystems
>
> Actually the sources seem to already contain zlib.
>
> So I assume we almost have a working doublespace already. But somebody ought
> to have a look at it to make it complete/fix the bugs.
>
> Imre
>
> >----- Oorspronkelijk bericht -----
> >Van: Imre Leber [mailto:[EMAIL PROTECTED]
> >Verzonden: vrijdag, maart 28, 2008 01:05 PM
> >Aan: [email protected]
> >Onderwerp: Re: [Freedos-devel] compressed FAT filesystems
> >
> >
> >Actualy like Eric, privately, pointed out we already have a driver to treat
> >a file as a volume, nl. SHSUFDRV.
> >
> >However, the problem is not the driver, but what kind of file system should
> >be used by such driver to make it compressed.
> >
> >We might just take SHSUFDRV and, like doublespace, assume that anything that
> >is on it is compressed. Then add a compressor like LZO to
> >compress/decompress everything going in and out. That way the file system
> >does not even need to be changed.
> >
> >Imre
> >
> >
> >>----- Oorspronkelijk bericht -----
> >>Van: Antony Gordon [mailto:[EMAIL PROTECTED]
> >>Verzonden: vrijdag, maart 28, 2008 10:11 AM
> >>Aan: [email protected]
> >>Onderwerp: Re: [Freedos-devel] compressed FAT filesystems
> >>
> >>I've read all the posts, now lets look at what DriveSpace/DoubleSpace
> >>actually did...
> >>
> >>You take a hard drive of x capacity, analyze the free space, a 'CVF'
> >>(Compressed Volume File) with variable cluster size, move the files on the
> >>disk into the newly created CVF file, compressing them in the process. once
> >>the files have been moved into the CVF, it is mounted as a drive letter,
> >>and if the file extension is .000, the drive letter is swapped with the
> >>host drive. accessed through a block device that connects to a MRCI
> >>(Microsoft Realtime Compression Interface) server.
> >>
> >>When I read about CVF and MRCI in the DOS 6 Programmer's Reference
> >>(Microsoft), I thought that there had to be a much simpler way to implement
> >>this. Especially after the lawsuit between DOS 6.0 and DriveSpace's
> >>appearance in DOS 6.22. Of course, other things pressing I never really sat
> >>down to come up with something, by that time Windows 95 was on the horizon,
> >>and you could at least get up to an 800MB hard drive, and Disk Manager
> >>could help you use it all.
> >>
> >>To effect the same principle in FreeDOS, a real-time compression interface
> >>would have to be clean room designed based on the known aspects of
> >>DBLSPACE/DRVSPACE integration with MS-DOS (or Stacker's integration with
> >>MS/PC-DOS), perhaps in the process figure out how we can improve the
> >>design, there is no need to be compatible, offer existing
> >>DBLSPACE/DRVSPACE users a reliable migrate path and go from there.
> >>
> >>
> >>
> >>
> >>
> >>> Date: Fri, 21 Mar 2008 14:08:34 -0430
> >>> From: [EMAIL PROTECTED]
> >>> To: [email protected]
> >>> Subject: Re: [Freedos-devel] compressed FAT filesystems
> >>>
> >>> Would be OK something like a tar file, that includes time, date and
> >>> attributes for each file.
> >>> And may be compressed if needed.
> >>>
> >>> +-+-+-+-+-+-+-+
> >>> Marco A. Achury
> >>> Tel: +58-(212)-6158777
> >>> Cel: +58-(414)-3142282
> >>> Fax: +58-(212)-2410828
> >>> Skype: marcoachury
> >>> www.geocities.com/marcoachury
> >>>
> >>>
> >>>
> >>> Imre Leber escribió:
> >>> > But then again,
> >>> >
> >>> > Do you realy need a file system if it is read only. You could just as
> >>> > well use a table in the front that lists file names with path, and copy
> >>> > all data after it. No need to have anything remotely like FAT and the
> >>> > like.
> >>> >
> >>> > Just:
> >>> >
> >>> > \temp\file1 start at 0
> >>> > \temp\file2 start at 1000
> >>> >
> >>> > 0: data for \temp\file1
> >>> > 1000: data for \temp\file2
> >>> >
> >>> > Not realy a file sytem, but should about the same.
> >>> >
> >>> > Imre
> >>> >
> >>> >
> >>> >
> >>>
> >>>
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> >>
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