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Subject: Re: How much HD space left?
From: Andreas Stemmer (groovingandi_at_gmx.de)
Date: 2004-03-24


Björn Stenberg wrote:
> The problem is that Microsoft Windows doesn't update this entry correctly, they are using an undocumented entry somewhere else. The freecount entry can be recalculated by Rockbox (in debug->disk info->free space), but it's too much work to do automatically each boot.
>
> If you or anyone else has more info about this, there are many of us who would like to hear it.

I guess you already have had a look at
http://www.microsoft.com/hwdev/download/hardware/fatgen103.pdf

The chapter about the fsinfo structure (page 21) says:

"FSI_Free_Count: Contains the last known free cluster count on the
volume. If the value is 0xFFFFFFFF, then the free count is unknown and
must be computed. Any other value can be used, but is not necessarily
correct. It should be range checked at least to make sure it is <=
volume cluster count."

and page 18 says:

"The list of free clusters in the FAT is nothing more than the list of
all clusters that contain the value 0 in their FAT cluster entry. Note
that this value must be fetched as described earlier as for any other
FAT entry that is not free. This list of free clusters is not stored
anywhere on the volume; it must be computed when the volume is mounted
by scanning the FAT for entries that contain the value 0. On FAT32
volumes, the BPB_FSInfo sector /may/ contain a valid count of free
clusters on the volume."

Perhaps Windows really scans the free clusters each time it boots?

Andreas

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