Operating system on a external harddrive

The title says all.
I got a 1.5 terabyte external harddrive and i was wondering if u plug it into the usb port can i install a operating system on it and use it?
Answer #1
You can but it’ll be very impractical so i don’t recommend it,First of
external HDDs (unless ESATA) are much slower then internals
and this is especially noticeable when running an OS from one,Second
of OS’s tend to get a lock on the hardware,Not sure what your purposes
are but if you think you can just install an OS and take the HDD with ya
and plug it to other computers it’s not gonna fly.
Answer #2
Ok then.
Because i would like to get a fresh windows on this pc but am not allowed to reformat due to family files.
Answer #3
Just backup those files then,Sit with each family member and have em
pick what they need.
Answer #4
Ive done exactly what you are suggesting to do with a drive. as long as it can be recognized by the computer you are plugging it into, as a spare drive letter, through your usb connection. A multiboot setup will also allow you to install another OS through a USB connection, and boot up to it later on. Installing to a USB with a setup disk can put your other drives at risk, if not done correctly.. Alternatively, you can clone another drive through and onto a USB connected drive. It will take a LONG while before the process finishes under either condition.=) Very Slow!
I had to use an additional piece of hardware to interface between the USB connection and the external drive. Unless you are using an external drive enclosure device, may work. A bare drive to USB connection may never work at all.
Answer #5
Why not partition the existing HDD, install an OS on the partition & use a boot manager?