Unix has had sparse files for a very long time, and periodically they cause confusion andheartburn. At a low level, the possibility for sparse files is moreor less inherent in the ability to have files that are not physicallycontiguous on disk; once you have non-contiguous files you need away to map from file offsets to disk blocks, and once you have thisyou can have sections that don't map to any blocks at all. All ofthat's fine, but a more interesting question