Q: If a portable hard drive is 3.5", does that mean that it is a desktop hard drive? And if it is 2.5", it's a portable one?
A: 3.5" would mean desktop hard drive that will probably fail pretty soon since it isn't designed to be moved around constantly. 2.5" would mean laptop hard drive that actually has a chance of lasting a decent amount of time since it is designed to be moved constantly (laptop drives are better built than desktop drives, which matters a great deal when a hard drive is external and gets moved between computers a lot).