I have UBUNTU 12.04 LTS OS. Its not an image file/ISO image. I have searched a lot about how to make a pendrive bootable in order to install ubuntu, but everywhere they assume that I have ISO file. Even I've seen How to make bootable pendrive to install ubuntu os?. So I'm confused as I don't know how to get boot manager to make my pendrive bootable.
REMEMBER: My UBUNTU copy is NOT an ISO image file.
Simply copy-pasting those ubuntu files is not working.