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bios ?

Posted: Thu Apr 07, 2011 3:27 pm
by Sam111
I have a bios that supports booting from usb.
I have 2 usb harddrives one is older then the other.
I can successfully boot my OS that was installed on the older usb hardrive but not the newer one.

I have 2 main questions

Question 1
I am wondering how the bios is able to access and boot from a usb. Does it still use the int 13 extended command in some way. What is the hex value given to a usb hardrive(i.e 80h is primary harddrive ,..etc etc). How does the bios assign numbers to usb devices and access them? ( assuming it is similar to floppy, harddrive, optical drive ,...etc)

Question 2
one harddrive is usb 2.0 but the newer one is usb 3.0 ( I know they should be backwards compatible but would this lead to any problems)
I am wondering if their is away other then trying to find a firmware update for my bios that would work for both devices.

I know both operating systems on the 2 usb harddrives are good because both work on my parents "new computer" which supports booting from usb.

Re: bios ?

Posted: Fri Apr 08, 2011 12:54 pm
by turdus
Sam111 wrote:I have a bios that supports booting from usb.
I have 2 usb harddrives one is older then the other.
I can successfully boot my OS that was installed on the older usb hardrive but not the newer one.

I have 2 main questions

Question 1
I am wondering how the bios is able to access and boot from a usb. Does it still use the int 13 extended command in some way. What is the hex value given to a usb hardrive(i.e 80h is primary harddrive ,..etc etc). How does the bios assign numbers to usb devices and access them? ( assuming it is similar to floppy, harddrive, optical drive ,...etc)
You can use the extended int 13 that operates by lba-packets. Usb devices would have number 0x80 and upwards, unless your bios supports several emulation methods (last week I saw a bios that allowed to do so, in the menu I could choose "usb emulation" to be floppy, removable media, and hard disks. I suggest to use hard drives).
Question 2
one harddrive is usb 2.0 but the newer one is usb 3.0 ( I know they should be backwards compatible but would this lead to any problems)
I am wondering if their is away other then trying to find a firmware update for my bios that would work for both devices.

I know both operating systems on the 2 usb harddrives are good because both work on my parents "new computer" which supports booting from usb.
This should work as you expected, if you have troubles maybe your bios' usb 3.0 implementation is buggy, you should try to update firmware