Things to consider when booting from USB

bloodhound23 · Post by **bloodhound23** » Wed Feb 06, 2008 2:23 pm

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.

cyr1x · Post by **cyr1x** » Wed Feb 06, 2008 2:30 pm

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.

bloodhound23 · Post by **bloodhound23** » Wed Feb 06, 2008 2:57 pm

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.

jerryleecooper · Post by **jerryleecooper** » Wed Feb 06, 2008 3:03 pm

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.

Ready4Dis · Post by **Ready4Dis** » Wed Feb 06, 2008 4:52 pm

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.

Dex · Post by **Dex** » Thu Feb 07, 2008 10:45 am

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.