Installing linux on external hdd

Hello all. I have a external hdd and i was wondering if i could install linux to it and just plug in the hdd when i want to use linux. Will there be any noticable performance decrease using a 5400 rpm drive via usb3?

I've installed Ubuntu and Mint on plenty of USB flash Drives. I don't see why you couldn't put it on an external HDD. As for performance you will probably have some slower read/write speeds (I recommend creating a 4 or 8GB partition for swap space) but nothing too serious.

So if i were to plug in the external drive it would go into the dual boot screen and if it werent plugged in it would just go right to windows

it depends on you BIOS Boot configuration. you would prob need to either manualually select it on the startup screen by hitting f12 or f10 or change the boot config so that removable devices are ahead of your boot drive.