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Things to consider when booting from USB
Posted: Wed Feb 06, 2008 2:23 pm
by bloodhound23
Ok, I want to make my OS boot from USB. Is there anything that changes when you boot from usb, compared to booting from a hard disk.
Posted: Wed Feb 06, 2008 2:30 pm
by cyr1x
I think booting is no problem but if you switch to protected mode you won't be able to load files from it unless you write a USB driver or setup VM86 and use the int's.
Posted: Wed Feb 06, 2008 2:57 pm
by bloodhound23
I'm entering long mode! Anyway that is no different than if you were booting from a HD, no BIOS ints to help you out.
Posted: Wed Feb 06, 2008 3:03 pm
by jerryleecooper
cyr1x wrote:I think booting is no problem but if you switch to protected mode you won't be able to load files from it unless you write a USB driver or setup VM86 and use the int's.
Unfortunately, using int 0x13 doesn't seem to work in vm86.
You need to write the drivers.
Posted: Wed Feb 06, 2008 4:52 pm
by Ready4Dis
Yeah, you'll have to make sure you have USB Mass Storage device drivers imlpemented in order to read the device after boot, but as far as the bootloader, there is no change, the bios treats the USB drive as a standard drive via int 0x13.
Posted: Thu Feb 07, 2008 10:45 am
by Dex
You can go to and from pmode to realmode, to read/write to usb fob, this work well. But it very slow, and the slow is nothing to do with going back and forth.