This means that your information cannot be accessed by anyone without your password, even if the device is completely opened up. Because both devices require no installation, you can use them on any PC. Both the HDPNC-U and the HDPNC-HSU have a button on the side that opens the device and allows you to quickly bring up the password screen. If the password has been guessed incorrectly one hundred times in a row, the device will permanently lock. At this point, it needs a re-initialization to work again. The shock-resistant body of these devices makes them able to put up with a little abuse (both have passed the standard 70 cm drop test). Both devices are compatible with USB 2.0 and USB 1.1 interfaces. The difference between this HDPNC-U and the lower cost HDPNC-HSU is that this HDD is ten grams lighter (310g as opposed to 320g), and is compatible with Mac operating systems 10.3 and older (once the device is reformatted). The I-O Data HDPNC-U 500GB HDD comes with a three year warranty.