Read/Write in Reserved Sectors of FAT32 Boot Record

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Hi,
I'm developing an application for interfacing with pen drive. I got handle and successfully Read & Write into the sectors. I need to Read/Write values in the reserved space of the drive. In the FAT32 Boot Record, there are reserved sectors in the offset 0Eh. Can i read/write in these reserved sector?. If so how can i do it?

Regards
Mohan

Posted 11-Jan-11 0:46am

Mohanraj Sam

Updated 11-Jan-11 0:54am

User 7429338

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User 7429338 · Answer 1 · 2011-01-11T01:00:00

Solution 1

You can use this[^] article to learn about accessing sectors on disk directly.

Considering you specifically ask about writing in reserved sectors, I'll assume you're familiar with the FAT32 file system. Either way, making a back-up of the drive would probably be a good idea.

Posted 11-Jan-11 1:00am

User 7429338

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Mohanraj Sam 11-Jan-11 7:10am

Hi Jones,
Thanks for ur reply. Actually I used ReadFile()/WriteFile() for read/write operations. If i need to write values in the reserved sector of FAT32 of offset 0Eh, how shall i mentined this address in the WriteFile() because it gets only the sector number.

Regards
Mohan

[no name] 11-Jan-11 7:24am

I added a reply in a new answer for you.

Espen Harlinn · Answer 2 · 2011-01-11T01:12:00

Solution 2

Once more a short description
http://support.microsoft.com/kb/100027[^].

Here is a link that you will find usefull:
http://en.wikipedia.org/wiki/FAT32#FAT32[^]

Regards
Espen Harlinn

Posted 11-Jan-11 1:12am

Espen Harlinn

User 7429338 · Answer 3 · 2011-01-11T01:24:00

Solution 3

The mentioned 0Eh offset is a byte offset within the boot record containing the number of reserved sectors.

The first reserved sector is sector 0, so any offset from 0 to the number of reserved sectors multiplied with the sector size in bytes, will be in a reserved sector.

Using the code from the article I linked to, you'd want to specify the offset in the Windows NT read/write functions like so:

SetFilePointer(hFloppyDisk,offset,0,FILE_BEGIN);

For example, let's assume we have sectors with a size of 512 bytes each and let's say you'd want to access sector 3. You'd want to set the file pointer like so:

SetFilePointer(hFloppyDisk,3*512,0,FILE_BEGIN);

Posted 11-Jan-11 1:24am

User 7429338

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Mohanraj Sam 12-Jan-11 0:24am

Thanks Jones. I unable to read intermediate data in the sector. That is i want to read data starting from the offset OEh in the first sector. I tried with the below code,

startinglogicalsector = 1;
SetFilePointer (hDeviceHandle, (startinglogicalsector*14), NULL, FILE_BEGIN);
ReadFile (hDeviceHandle, buff, 512, &dwBytesRead, NULL);

But I get all the values of first sector starting from 0th offset. How can i read from 0Eh offset of 1st sector.

Also i have another question, 0Eh offset represents "Reserved Sectors". Is it gives total number of reserved sectors count or i can use that offset as reserved space. If it says about the count then how can i know which are the sectors are reserved. Any idea about this.

Regards
Mohan

[no name] 12-Jan-11 4:43am

The value stored at byte-offset 14 (0Eh) is a 2-byte sized variable holding the number of reserved clusters.
It's a value, for example 3. This means 'the first 3 sectors are reserved sectors'; it doesn't mean 'sector 3 is a reserved sector'.

If you know the sector size, which is stored as a 2-byte value in sector 0 at byte-offset 0Bh, you can calculate the amount of reserved bytes. Suppose the sector size would be 512, then the amount of reserved bytes is 3*512 = 1536. Any offset used with SetFilePointer from 0 to 1536 will put you in reserved space.