Both Blu-Ray and HD-DVD are blue laser based and as such are, by themselves, incompatible with present day red laser DVD; however each format's consortium requires all players to be compatible by implementing a separate red laser within the player; so players of both formats are backward compatible to the end-user;

Be aware however that Blu-Ray and HD-DVD are incompatible formats to each other at the disk format (pit) level (that's how Blu-Ray exceeds HD-DVD storage capacity); so universal drives that support both formats are prohibitively expensive, requiring 2 completely seperate drives (despite the fact that the format processing chips being manufactured support both formats at the data level); In addition, each consortium has stated they will disallow manufactures to license both within the same machine (for now);

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