MPEG-4 SLS allows for having both a lossy layer and a lossless correction layer similar to Wavpack Hybrid, OptimFROG DualStream and DTS-HD Master Audio, allowing for backwards compatibility to MPEG AAC-compliant bitstreams. MPEG-4 SLS can also work without a lossy layer (a.k.a. "SLS Non-Core"), in which case it will not be backwards compatible, Lossy compression of files is necessary for files that need to be streamed to the Internet or played in devices with limited storage. With DRM, ripping of the lossless data or playback on non DRM-enabled devices could be disabled. MPEG-4 SLS is not related in any way to MPEG-4 ALS (Audio Lossless Coding).