An Enhanced CD (ECD), also known as CD-Extra or CD-Plus, is a hybrid compact disc format that integrates standard digital audio tracks with multimedia data, such as videos, images, lyrics, and interactive content, on a single 120 mm optical disc, enabling playback of music on conventional audio CD players while unlocking additional computer-readable elements via CD-ROM drives.[1][2]Developed jointly by Philips and Sony, the format adheres to the Blue Book standard, which was finalized and released in version 0.9 in July 1995 to standardize mixed-mode CDs and overcome compatibility issues with earlier experimental discs that combined audio and data in a single session.[2][1] The initiative involved collaboration with Microsoft and Apple to ensure broad support across operating systems, aiming to leverage the growing prevalence of personal computers equipped with CD-ROM drives in the mid-1990s.[1] The Recording Industry Association of America (RIAA) trademarked the term "enhanced CD" following a protracted standardization process, marking its commercial push amid the digital music revolution.[3]Technically, an Enhanced CD employs a multi-session structure: the first session contains up to 98 Red Book-compliant CD-DA audio tracks for uninterrupted playback on any standard CD player, while the second session holds CD-ROM XA data tracks formatted under ISO 9660, supporting elements like MPEG still pictures, QuickTime videos, and hyperlinks (primarily for full albums).