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 Post subject: MBR Bootcode on FAT32 HDD
PostPosted: February 2nd, 2009, 19:30 
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Joined: February 2nd, 2009, 18:14
Posts: 4
Location: Germany
Hi everybody,

at the moment I'm trying to analyse what exactly the formating of a partition in FAT32 does. I know, that has been done before, but I learn better by doing it on my own. :)

Know I realized that the Boot Code in the Volume Boot Record matches exactly to what I find in the Internet. But not the Code in the MBR.

What I did ist this:

-1- Write 0x00 to every sector using dd if=/dev/zero.
-2- create a primary partition.
-3- Format this partition with a Windows XP prof. SP2 OS to FAT32.

So this is a pure data storing HDD, no OS installed there.

Now my question :

where can I find the code explanation for an MBR with these specifications?

I looked at, for example, http://mirror.href.com/thestarman/asm/mbr/index.html
but they don't have the code i found...

I added a screenshot of "my" MBR.

Any ideas?

Thanks,

Erik


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File comment: MBR without OS / FAT32
FAT32_MBR_NO_OS.png
FAT32_MBR_NO_OS.png [ 67.62 KiB | Viewed 9886 times ]

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 Post subject: Re: MBR Bootcode on FAT32 HDD
PostPosted: February 3rd, 2009, 9:01 
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Joined: February 2nd, 2009, 18:14
Posts: 4
Location: Germany
Sorry, wrong screenshot. This is the actual screenshot and this is the typical Win XP MBR. I'm sorry, my fault. :(

Can be closed... better deleted :)


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MBR_FAT32_NO_OS.png
MBR_FAT32_NO_OS.png [ 726.77 KiB | Viewed 9886 times ]

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 Post subject: Re: MBR Bootcode on FAT32 HDD
PostPosted: February 3rd, 2009, 19:56 
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Joined: October 21st, 2005, 0:45
Posts: 1517
Location: Mexico
well if u want to know on deep what its this code,one way u can use Debug a powerfull tool :D command acccesing by Int13h , to unassembly it and let u know what does it mean the opcode 33 C0 and so so : if im remeber that means disable ints.after that setting stack to segment 000 ,setting stack to pointer 7C00 to load on that memory zone the MBR , im not sure :roll: that first bytes are the called Bootstrap code, then at offset 1B0 its starting the Partition table info,but the best its "unassembly" from this way u can understand what its happening on deep well u need to know assembly Opcodes to do that :) aaah!.. a little tip when u find " CD 13 " that means Int13h

55AA its the boot signature...

Regards


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 Post subject: Re: MBR Bootcode on FAT32 HDD
PostPosted: February 4th, 2009, 6:16 
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Joined: February 2nd, 2009, 18:14
Posts: 4
Location: Germany
Hi beto,

thank you :)

Erik

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 Post subject: Re: MBR Bootcode on FAT32 HDD
PostPosted: February 4th, 2009, 10:41 
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Joined: October 21st, 2005, 0:45
Posts: 1517
Location: Mexico
i got some free time & was reading my notes finally i find a usefull link, enjoy it http://www.ata-atapi.com/hiwmbr.html
by the way using debug u can got the MBR too or any sector , :)


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 Post subject: Re: MBR Bootcode on FAT32 HDD
PostPosted: April 1st, 2009, 12:11 
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Joined: February 2nd, 2009, 18:14
Posts: 4
Location: Germany
Hi beto,

sry for the delay... thank you very much for your link :)

Erik

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 Post subject: Re: MBR Bootcode on FAT32 HDD
PostPosted: April 2nd, 2009, 9:38 
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Joined: October 21st, 2005, 0:45
Posts: 1517
Location: Mexico
u´r welcome :wink:


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 Post subject: Re: MBR Bootcode on FAT32 HDD
PostPosted: April 6th, 2009, 17:28 
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Joined: December 12th, 2008, 17:00
Posts: 181
Location: Cook islands
This is fully described it the Data Extractor documentation, I learnd if from there.

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