Zusynoid-x wrotethere are many other ways to protect your HDD from viruses, running a whole freaking OS on it is not the most practical of solutions
spend some time on google you WILL find your answer
I would be crazy to put an entire OS on it just to protect it from viruses, but what I want from an OS is like a portable computer in my pocket, (all my programs, files, pics all running and installed on an HDD system)
EDIT: It seems impossible to protect an external HDD from a virus, the problem is I need it to be plugged in viral and infected computers, especially for project presenting in school.