Hello, i tried to post on alt.os.development but google has more problems everytime.

I have write a boot sector that loads a file (Os kernel) from a subdirectoire
in a fat32 partition, instead of using bios that is limited to 8GB on most computers ,i have included a ide driver wich uses lba48 ,the ports adress are hardcoded ,so if i change the disk from ide1 to ide2 it will not work, to solve this i will try all combinations in the same order that the bios uses,
but i'm not sure if all the bios use the same order , for example if master
disk on first ide controller is not present , the bios will try to boot slave disk on first controller or master disk on second controller?
exits a better way to know wich port i have to use?
note that i need a simple solution, because 400bytes for code is not very much.

I do not think that the order really matters
This order is for the user to setup in the BIOS

If your OS was loaded from a HDD then you can continue from there
And you do not have to do everything in the first 512bytes; you can load a seconday stage code... and there you will have more space for your loader code.

You might want to try drive BIOS function 42h. See http://www.ctyme.com/intr/rb-0708.htm. On the systems I have tested (5 years old and newer), this function reads hard drives larger than 132GB without any trouble.

As far as finding the IDE controller I/O port, newer computers that boot from SATA controllers can use almost any port, so hardcoded addresses wouldn't work. If you wanted to make things really complicated (yes, I know you don't, but let's just pretend), you could have your boot sector code load additional sectors from the first track (which is otherwise unused) and have a nice complicated program that queried the PCI bus or Boot BIOS Specification (http://www.phoenix.com/NR/rdonlyres/56E38DE2-3E6F-4743-835F-B4A53726ABED/0/specsbbs101.pdf).

Anyone has understand the problem.
first: i can´t use the bios because on 2 of the 3 computers i have at home
the bios has the 8Gb limit (64bit lba service is not implemented)
second: my os don´t have his own partition ,it uses a windows fat32 partition and i don´t want to overwrite current boot sectors, my boot sector is stored in a file and its loaded by windows multiboot loader, and loading a second stage loader has more problems that loading the kernel because i don´t want to reserve fixed sectors, only files. and why would i
make a second stage boot loader if i can do all i want in one sector.
finally the boot program test the 4 ide drives using ports 1f0h 170h those ports are more standard than the bios, y have already tested and works like i want.

of course i could do like windows and put a second stage boot loader on the first partition below the 8GB limit ,but this solution don´t works if the
first partition is like ntfs not supported by my OS.

Octavio, the boot order defined by the BIOS is BIOS specific. In the older days you could only boot of the Primary Master. Ignore the boot order because newer bios's support booting of network cards, flash discs, etc. You can set which drive to boot from as well. Maybe have a look at the GRUB documentation referring to the Multiboot specification.

Whatever order you implement will be up to you to define.

I´m talking about the hard disk only , and have seen any computer wich boots first the slave hard disk if a master disk is present.
Since the boot sector is placed on the hard disk ,i don´t have to worry about other boot devices, for other devices i use another boot code.
I´m not sure but i think that grub uses the bios, so it has the bios limitations.