MotoX 2014 has 24GB out of 32GB available Keeping in mind that the same OS (Lolipop) runs on MotoG which can be 8 GB, how can it be that OS takes up 8 GB? MotoX comes with only a couple of extra software, which surely cannot much space…
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Try to do a factory reset. If your memory is still such 'low' comparing it to the other models then it's just the way it is. Flashing the entire stock image may be a good thing to do since it may be firmware related.