Hi, again.
External drives are usually the exact same drive as the one you install in your computer, except they are enclosed in a case.
They have the same spinning platters and read/write heads and have the same potential for failure.
There is something called a “solid state drive” sold, which actually has no (I think) moving parts.
These drives have smaller capacities than the traditional type does, and may cost a bit more, too.
They are sometimes used to store system data (so the PC starts faster), while application data is stored on a traditional HD.
I don’t know if they are sold as external drives, but there are kits that you can create your own from if they aren’t.
You can also possibly use a USB memory key. I think some pretty high capacity ones are sold nowadays, but I don’t remember specifics about size and price.
I don’t know how reliable one type of storage is over the other. I have heard of USB memory devices failing – they’re not infalible.