the size, 2.5" hdd are genrally for laptops and make nice externals due to their size however 3.5" ( the standard desktop pc hard drive type) will have the option of larger capacity and are physically bigger. in most cases 2.5" wont need an external powerpack, however 3.5" will.
06/07/2008
'sick of answering simple questions over and over and over again that you can find on google'