The NSLU2 is a small and silent, ARM CPU powered network storage server that does not have disk storage built in - you need to attach one or two external USB hard drives to it's USB connectors on the back. It is one of the many relatively cheap solutions for out-of-the-box network storage demands. It has a spartan administrative user interface, and is not customizable. However, it's firmware is built on Linux so the source code modifications have been made available to the public. Initially, there was only the “unslung” firmware alternative which enables you to add additional software to the device