Re: [plug-newbies] OT: MBR programming

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Author: Philippine Linux Users' Group (PLUG) Newbies Discussion List [DEPRECATED]
To: Philippine Linux Users' Group (PLUG) Newbies Discussion List [DEPRECATED]
Subject: Re: [plug-newbies] OT: MBR programming
----- Original Message -----
From: charkee berekeke
To: Philippine Linux Users' Group (PLUG) Newbies Discussion List
Sent: Thursday, December 15, 2005 9:33 PM
Subject: Re: [plug-newbies] OT: MBR programming

>i was just wondering if i could recreate the mbr so it would boot by
>default on a
>specific OS, say 98, but will execute a bootloader if a certain key is
>pressed during
>a certain interval in the boot-up process. I only want to restrict use of
>an IBM-PC.

yes you can... all you need is an assembly language programming...

after the power on self test (POST) by the bios.... it calls INT 19... it
reads the MBR (cylinder 0, head 0, sector 1) and put the code at segment
0000 offset 7c00 (0000:7c00)... then INT 19 jumps at that segment-offset
location and executes the code of MBR... the code of MBR relocates itself at
segment 0000 offset 0600 (0000:0600) and continues execution there... MBR
will read the boot sector of the assigned active partition and put at
segment 0000 offset 7c00 (0000:7c00)... after that, execution transfer there
and the rest of the code will take care for that OS..

you can do what ever you wanted to do as long as you understand how the boot
up sequence works... i manipulated the mbr during my college days when i
wrote my boot virus...


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