An image sensor includes a photoelectric conversion region formed in a substrate, an interlayer insulation layer formed over a front side of the substrate, a carbon-containing layer doped with impurities and formed over a back side of the substrate, and a color filter and a micro-lens formed over the carbon-containing layer. The rack server system includes a battery backup unit and at least one server. Each fin is preferably formed longitudinally along the aft portion of the chine and extends below the waterline. In a first reed valve, an opening end is disposed upward and a fixed end is disposed downward. Before deleting a version on the backup storage, the retention manager determines whether deletion conditions are met.