This guy converted a Moleskine journal into a hard drive enclosure (Yes, he knows it won't dissipate heat very well. He doesn't care and neither do I).
A few weeks later I accidentally placed my WD Passport external drive on top of my Moleskine notebook and, what do you know, they were pretty much the same size. That got me thinking.
After some extensive research (well, I just googled for 2.5" sata enclosure) I found all I needed: an external enclosure for laptop SATA drives that would not need a power supply and with the smallest possible circuitry. There are many brands and models, but this one from Cool Drives was just perfect, and at under $25 it was cheap enough I didn't have to ask my wife for budgetary allowances.
