After Success of Backtrack Distribution of Linux Operating System ,Backtrack become most popular penetration Testing tools for Security Expert and Even white hat hacker.
Backtrack 5 is become more popular but suddenly it is discontinued and new OS came in market, i.e. Kali Linux.
Kali Linux is more powerful than Backtrack and included advanced tools.
You can run this Operating System in two mode
2. installed mode.
Live mode is best way to run Kali Linux in any computer System. For Booting from USB there are many Software available like unetbootin.
but if you are using unetbootin for Kali linux then it will give you an error at the time of Booting. Unetbootin was best for Backtrack . So i am telling you a software which will work best for Kali Linux.
Universal USB Installer.
Universal USB Installer is best if you want to run kali linux from USB.