Mixed Mode aka Track One
These put CD-ROM data on the first track, followed by music data, which plays on any audio CD player. The system works well, although some older CD decks may try and play the CD-ROM data, resulting in a blast of white noise through the speakers. For this reason, most Mixed Mode CDs have a warning sticker telling audio CD users to skip the first track.
CD-ROM Ready aka Track Zero
CD-ROM Ready is designed to avoid the Track One problem. It works by hiding the CD-ROM data in the pre-gap, which is just before the first track. The pre-gap is normally around two seconds in length, but CD-ROM Ready discs extend this to 30 minutes or more. Several systems use the pre-gap including Ardent Records' AudioVisual CD, Aix Entertainment's i-trax and Active Audio, developed by PAMS and BMG.
Another advantage of CD-ROM Ready is that CD-ROM owners don't need additional software to use them. However, some CD-ROM drives, notably those from NEC, cannot read this type of disc.
CD Plus aka Track Two
CD Plus has been developed by Philips and Sony, with help from Apple and Microsoft. The CD Plus standard, known as the Blue Book, is a mix of CD audio (red book), CD-ROM (Yellow Book) and multisession (Orange Book) standards.
A 50-60 minute music CD has around 200 Mbytes of spare data which can be used for pictures, text, sound and software-based video like QuickTime or Video for Windows.
The system works by recording music data in the first session and data in the following one(s). Music CD decks simply play the music and ignore the CD-ROM data, while CD-ROM drives play the extra information. However, only around 65 per cent of the world's CD-ROM drives are multisession-compatible, and those that are may need additional software drivers to play the discs.
Microsoft has made Windows 95 compatible with CD Plus, and Apple's latest CD software also recognises the new discs.
Other Discs
Rainbow CD
Developed by Philips, it's a Track One disc designed to play on audio CDs, PC and Apple CD-ROM drives and CD-i decks.
Video CD Plus
Developed by OmniMedia, it mixes interactive programs with a linear video programme. The video plays on any Video CD deck, and the extra data can be seen on a PC with a MPEG card and CD-ROM drive. Some Video CD Plus titles will contain software-based MPEG-1 video and a Web browser.
CD-i Ready
A format that mixes red book tracks, which play on any music CD, and Green book tracks, which are read by a CD-i player.
CD Plus Graphics (CD+G)
Part of the original Red Book audio CD standard, it uses spare subcodes to display teletext-type words and pictures on a TV screen. Mainly used in Japan for karaoke.