I need to purchase an external hard drive for back purposes.... confusion though is in some of the terminology on these drives.

of the 2 external hard drives i'm seeing one just says EXTERNAL hard drive and seems to have a bigger foot print than the other one which says PORTABLE external hard drive.

aren't they both PORTABLE hard drives.... and why is the one with the larger case/footprint cheaper and has a larger capacity than the "Portable" drive??