OSDev.org

Hi,

I have followed the baby step 2 at http://wiki.osdev.org/Babystep2 listed on the tutorial page of osdev.

I compiled the code using :
and then wrote it to a USB device using the dd command:
When I use the USB to boot, sometimes the BIOS recognizes the USB as FDD and some times as HDD. When the USB is recognized as HDD it does not boot. I tried this on a lenovo thinkpad x220 which has both USB-FDD and USB-HDD in its boot list and the USB-FDD has a higher priority, when I press F12 the USB shows up as USB-HDD.

Thanks,
Karim.

If you look at the binary layout of the first 512 bytes, there is neither a BPB nor a partition table (MBR).

The BIOS does not know how it should handle it.

Hi,

So you mean it is up to the BIOS, and that is why some BIOS will detect it and some others will not.

So to make sure I understand, if I add the FAT12 BPB to my boot sector and copied it to a flash it should work and detect the FLASH as USB-FDD, right?

Thanks,
Karim.

kemosparc wrote:if I add the FAT12 BPB to my boot sector and copied it to a flash it should work and detect the FLASH as USB-FDD, right?

There is no warranty. It depends on the BIOS implementation. Having a valid "floppy-like" structure just makes it more likely.

This in some cases can be changed in the bios usb device emulation. Like fdd hdd optical, etc. Try to take a look at bios and find it.
i hope this helps.

Good luck.

Hi,

Actually the only think that I can do is to add them to the boot list. But the USB type isdetected at boot time and the type is selected and displayed accordingly.

Thanks
Karim.

If there is BIOS Parameter Block in first sector of USB drive, BIOS usually detects it as Floppy otherwise as a Hard disk.