how can we make usb drive bootable

Originally Posted by RedSon

Linux cannot make a drive bootable, it is your BIOS that does that. You will have to fiddle around with your BIOS settings.

Originally Posted by Nepomuk

Actually, that isn't quite correct - you do need a Boot sector, if you want to boot something directly from the drive (in Linux and Windows since 2000 I think) that would normally be: load a bootloader).

This page contains something about making a partition theoretically bootable, but then you'll have to install a bootloader (like syslinux, grub or lilo) on there too. There's a quite detailed article about the whole process here.

Greetings,
Nepomuk

Originally Posted by RedSon

Yes but you still need to change your settings in BIOS to try a USB drive before a hard drive or a disc drive.