7 things you didn't know about Blu-ray

The Blu-ray Disc format packs in more data than a normal DVD or CD

1. The Blu-ray Disc (BD) format takes its name from the laser used to read (or write to) the discs. It works in the part of the spectrum and functions at a finer wavelength compared to the red lasers used for normal DVD or CD. As a result, more data can be packed in.

2. Some newer Blu-ray players include picture-in-picture features and a wider range of alternative audio tracks. These can be switched more easily by accessing a part of the menu without interrupting the film.

3. Another feature in the works is BD-Live. When you play certain discs you may be able to download new extras via broadband added since the disc was made. There could also be social networking features that inevitably go with internet-connected hardware.

4. Blu-ray Discs are single or dual-layered, offering a maximum capacity between 25-50GB. Almost all players handle dual-layer discs. Tests have been made with three, four, six and even ten-layered discs, pushing capacity to 250GB.

5. JVC has invented a multilayered dual-format disc combining a normal DVD with a dual-layered BD on the same side. This is similar to hybrid CD/SACDs or the double sided DVD and HD DVD releases out now.

6. Blu-ray uses regional coding, like DVD, to control whether certain discs can be played overseas. Unlike DVD's six regions, BD uses three. They are roughly divided into the Americas and the Far East; Europe, Africa, Australasia and the Middle East; and Russia and Central Asia.

7. The BD specification only requires players to support the traditional digital audio formats of Dolby Digital, DTS and linear PCM. The latter is one way of getting up to 7.1 sound channels, but it is not space efficient. For this reason some of the latest BD releases support at least one of the newer optional HD-orientated formats: DTS-HD, Dolby Digital Plus and TrueHD.