What is main difference in a portable external HDD and a regular external HDD?
There's a small difference. A portable HDD draws power directly from your computer while an external HDD draws power from a power adapter plugged into the wall. Durability will vary depending on quality. If you're using a portable device (such as a laptop) it is suggested to use a portable HDD so you don't have to plug it in elsewhere. It should also be noted that portable HDDs draw more power from your computer which may result in faster battery consumption on portable devices or worse performance on devices using a very little amount of power (such as a Raspberry Pi).