A complex optical element includes a first optical portion and a second optical portion which are made of materials different from each other. An input latch circuit latches each bit data included in internal serial data by a strobe signal delayed by the variable delay circuit. The cache assignment that optimizes performance may be determined. The maximum width of the holes is equal to or less than the wavelength. The second casing has a second surface. Cache server computing devices segment content into an initialization fragment for storage in memory and one or more remaining fragments for storage in a media having higher latency than the memory.