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 Post subject: BIOS seems to boot even though the first sector is empty
PostPosted: Mon Nov 28, 2022 1:14 pm 
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Joined: Mon Nov 21, 2022 3:02 pm
Posts: 2
I read from the wiki and other sources online that the BIOS will always load the first 512 byte sector on a detected drive, with the
Code:
0x55aa
signature at the end. However, I found that from the iso produced when I use
Code:
mkisofs
, the first 512 byte sector does end with
Code:
0x55aa
, but it does not contain any code, it is all zeros. The actual bootloader is located at some other sector, which is confirmed by the boot sector location in the el-torito boot table. How does the BIOS successfully load the bootloader then?


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 Post subject: Re: BIOS seems to boot even though the first sector is empty
PostPosted: Mon Nov 28, 2022 6:45 pm 
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Posts: 631
moogloof wrote:
How does the BIOS successfully load the bootloader then?

moogloof wrote:
The actual bootloader is located at some other sector, which is confirmed by the boot sector location in the el-torito boot table.

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 Post subject: Re: BIOS seems to boot even though the first sector is empty
PostPosted: Mon Nov 28, 2022 6:56 pm 
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moogloof wrote:
I read from the wiki and other sources online that the BIOS will always load the first 512 byte sector on a detected drive

This applies to floppy disks, hard disks, and devices that behave like floppy or hard disks such as USB flash drives. This does not apply to optical discs.

You're booting an optical disc.


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 Post subject: Re: BIOS seems to boot even though the first sector is empty
PostPosted: Mon Nov 28, 2022 7:07 pm 
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Joined: Mon Nov 21, 2022 3:02 pm
Posts: 2
I see, thank you. That would also explain why it did not boot when I tried it on the media that you mentioned.


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