The PJB-100 is a portable MP3 player that uses a 2.5 inch notebook hard disk for its storage. In its basic configuration it'll hold about 80 hours of music, or about 100 popular music CDs. It's physically larger and heavier than flash-based players, but it has the advantage of being able to store a reasonably large music collection in one place.
It started out as a research project from Compaq's corporate research department, and has now been made into a product.
The PJB was licensed to a Korean company called HanGo ('Remote Solution' in the USA), and they have brought it to market. You can read more about it at the manufacturer's web site.
The Openpjb SDK
The PJBSDK is actually the core software and APIs that programs like PJBExploder, PJB.EXE, Dobber's great tools, and many others are based on. Its open-source, supported and enhanced by volunteers, and free and available for anyone who wants to write their own utilities. Normally, the programmers who are inclined to write their own tools, or work on the existing ones will get the SDK directory from the OpenPJB CVS repository. But that can be difficult for some. So periodically we released a pre-packaged version that can just be downloaded.