0caitlinsdad 9 years ago ReplyUpvotehttps://www.instructables.com/id/Build-an-External-Hard-Drive/ How to do it.http://www.geeks.com/products.asp?cat=CSE Where to get an external HD case.You can install your desktop hard drive (3.5 inch size) into a special case that has a USB adapter/connection to your laptop. It probably requires an external power supply since it will not have enough power through the USB. A smaller laptop drive may be powered off the USB alone or have the paired up USB connector to draw twice as much power. It will show up as another drive. Good luck.