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More songs into a CD.
Yes
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the firmware has to be done on the player, right?
ie. my mp3 player in my car won't be able to use these cds, right?
Yes,
but this does ex-clude CD-drives, unless they can read the finer structures somehow.
Any firmwareupgradeable (car-, portable or DVD-) players that uses a DVD-drive should be firmware upgradeable.
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) If CDs can be read faster,
Due to the higher data density & better error correction youre supposed to get somewhere arround 70-80x reading speed (Sanyo).
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that means less reading time = less battery consumption = more playback time
I'd asume that Spinup-time/-current of a drive will have a significant impact on power consumption if you need only a short read time vs. spinup. The larger your internal storage the more likely you'll see a benfit.