"Mastered in 4K" Blu-ray Discs can be played on all existing Blu-ray Disc players.

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Some existing CD-RW drives require that the whole CD-RW disc be erased before new data can be written to it.

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However, because the new media specifications are extensions of current Blu-ray Disc technology, future BDXL and IH-BD devices can be designed to support existing 25GB and 50GB Blu-ray Discs.

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