Sony expanded the PS one with an official five-inch LCD monitor that could be attached directly to the small console. The PS one and screen bundle appeared in 2001 and turned the compact PlayStation revision into an easily transportable system, although it still required an external power source. The screen incorporated stereo speakers and allowed the PlayStation CD-ROM catalogue to be used without relying on a conventional television. The basic PS one had appeared in 2000; 2001 refers to the commercial bundle with the LCD monitor.