The invention discloses an extension box of storage media, which mainly utilized a plurality of heat dissipation fins protruding from a bottom surface of a bottom shell of the extension box. The relative angle allows for regulation of the flow of fluid. Reuse distance for one memory operation may be measured as the number of memory operations that have been performed since the memory object it accesses was last accessed. A chain tensioning idler contacts the chain between the first idler and the second idler and is capable of movement in a direction transverse to the movement of the chain.