BIOS seems to boot even though the first sector is empty

[moogloof]

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: Select all

0x55aa

signature at the end. However, I found that from the iso produced when I use

Code: Select all

mkisofs

, the first 512 byte sector does end with

Code: Select all

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?

[klange]

How does the BIOS successfully load the bootloader then?

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

[Octocontrabass]

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.

[moogloof]

I see, thank you. That would also explain why it did not boot when I tried it on the media that you mentioned.