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How does FAT32 calculate free and used disk space ?

 
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andreluizeng



Joined: 04 Apr 2006
Posts: 117
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How does FAT32 calculate free and used disk space ?
PostPosted: Tue Mar 10, 2009 7:27 pm     Reply with quote
Hi,

I have this struct (FAT32 diskinfo)
Code:

typedef struct _diskinforec
{
   char      hJumpCode[3];
   char     OEMName[8];
   int16      hBytesPerSector;
   char      bSectorsPerCluster;
   int16    Reserved1;
   char      FATCopies;
   int16    hMaxRootEntries;
   int16    hSectors;
   char      Descriptor;
   int16    holdSectorsPerFat;
   int16    hSectorsPerTrack;
   int16    hNumberofHeads;
   int32     hNumberofHidden;
   int32    hNumberofSectors;
   int32    hSectorsPerFat;
   int16    hFlags;
   int16    hFAT32Version;
   int32    hRootStartCluster;
   
} diskinforec;


Anyone knows how to use it to calculates disk free and used space ??

Thanks in advance.

regards
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Andre
asmallri



Joined: 12 Aug 2004
Posts: 1634
Location: Perth, Australia

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Re: How does FAT32 calculates free and used disk space ?
PostPosted: Tue Mar 10, 2009 7:32 pm     Reply with quote
andreluizeng wrote:

anyone knows how to use it to calculates disk free and used space ??

thanks in advance.

regards


Its a painful process. You have to analyze the FAT to see how many clusters are unused then multiple by the number of sectors per cluster * 512

Used depends on you definition - if you want to know how much cannot be allocated then = total clusters - clusters used * sectors per cluster * 512

If you want to know how is used by files then you need to take into account clusters allocated and the unused sectors in the cluster.
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andreluizeng



Joined: 04 Apr 2006
Posts: 117
Location: Brasil

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PostPosted: Tue Mar 10, 2009 7:52 pm     Reply with quote
asmallri

Were those calculations that I was talking about.

thanks a lot.

best regards
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Andre
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