I have used-up all my free disc space on my PC. I have tried a Disc Clean-up but to no avail. There is nothing more for me to delete as I store thousands of photos on the HD. Here is my question: I see small portable hard drives available for under $100. If I purchase a unit and attach using the USB port, would that solve my problem? My PC is an Acer. Are all portable HDs compatible or must I buy a HD from Acer? I would hate to buy a unit only to learn that it is not compatible. Thanks.