The Road to KDE 4: Solid Brings Hardware Configuration and Control to KDE (KDE.News)
One of the many new technologies for KDE 4 is the often mentioned, but seldom explained Solid Hardware API. Hardware has always been a bit of an annoying element of using Linux and other Unix [like] operating systems, but Solid hopes to fix that for KDE 4. In many ways, Solid is like Phonon, in that it's a Qt/KDE style API around already existing components at the lower level, such as freedesktop.org's HAL. It is already quite functional in the backend, and it's already affecting visible KDE components."