The DVD specification does not define any particular type of player. As in CD, it is up to the player manufacturer to produce a device that will play DVD discs. This means developing an appropriate laser and optical read-out unit, the IC set needed for decoding, and a motor control servo. For dual-layer discs, the player needs a laser that can focus on either layer, and to be compatible with CDs - which all Philips players will be - a laser (or lasers) are needed to focus on both types of disc, with their considerably different focal lengths. (Philips, and particularly PKM's, know-how and strengths in development and production of optics, drives and engines, as well as ICs and other components are a strong foundation for creating optimal DVD player solutions) The driving force behind the multimedia revolution, MPEG1 compression technology opened the gates to full-screen movies and video sequences, with stereo sound, on CD-ROM and Video-CD. MPEG2, the system adopted for DVD, goes much further. Enhanced by a faster and dynamically-adaptable data rate, MPEG2 can compress a full-length movie (over 2 hours on a single-layer, single sided disc, and nearly double that for a dual-layer) into the large capacity available on a DVD disc. Not only that, but the picture is fully interlaced, giving a picture quality that is limited only by that of the TV set. The complementary audio system to MPEG2 Video is MPEG2 Compatible Multichannel Audio. This provides digital sound not only for the 5.1 loudspeaker configurations used in many Home Theatres, but even for 7.1 configurations, which are presently in movie theatres, but have yet to appear in Home Theatres. MPEG2 Compatible Multichannel Audio is also both-ways compatible with MPEG1 stereo: MPEG1 stereo can be played on MPEG2 systems, and MPEG2 can be played (as stereo) on MPEG1 systems. Analogue systems such as Dolby Prologic can also be accommodated. Another notable characteristic of MPEG2 audio is the large number of alternative sound tracks offered. Up to 7 tracks can be accommodated in stereo, and as many as 14 in mono. (An alternative digital sound system, Dolby AC-3, is also specified. This can handle 5.1 speaker configurations, and is also compatible with analogue systems.)